efficient 10m displacement powercat

[groper]

well im having second thoughts on the design of this 10m powercat... initially i had a lightweight planing hull idea but the prevailing conditions rarely allow for high speed travel so...

Now Im thinking more along the lines of 10m displacement hulls... i initially didnt consider a displacement hull as i want this to be a trailer boat and i didnt think a narrow beam would suit displacement hulls due to the negative wave interference. i can go upto 3.5m beam which is max daylight trailerable with oversize load permits etc.

Im hoping for an efficient cruise around 17kts, powered by 2x 50hp 4str outboards. Setup for day trips and the occational extended trip for a few days with minimal gear. LIghtweight construction of balsa and epoxy/glass laminate, i should be able to build this to around 1500kgs.

i think it just may be possible without too much negative wave interference provided we push this quite fast and it runs at high froude numbers above 0.8. Negative wave interference isnt supposed to be all that bad from what ive read at high froude number, as opposed to maximum interference wave drag occuring around Fn 0.5. So ive kept the hulls with a high beam/length ratio around 15:1 and low Cp in a hope we can operate it at high froude number to avoid the wave interference problem of the narrow hull seperation.

So this is what ive come up with so far... http://i439.photobucket.com/albums/qq120/gravitygroper/nicks-hulls.jpg

The waterline shown is with a displacement of 1000kgs per hull.
Cp=.55
DWL= 9.7m
beam @ DWL= .65m

I cant seem to get michlet to work from the freeship export file...? does anyone know what might be causing the problem? id like to get a power estimate for 17-20kt speeds...

I might have to look at increasing the beam/length ratio further to around 18:1 perhaps?

And once the design is finalized, what is the best way of getting the data out of free!ship for the bulkhead shapes at each station so that i can start building it?

Any other advice or ideas are welcomed.

Happy boating

[groper]

Im looking for ideas on;

Tunnel height clearance? - so far im thinking around 800mm from DWL.

Design ideas to combating "hobbie horsing"? - which i think is a challenge for a design like this.

Minimizing transom wave drag from squat under power? flatter or more buoyant aft hulls VS minimum cross sectional area designs? under power i dont think its possible to keep transoms clear of water in a balanced design that doesnt compromise other qualities???

[daiquiri]

I think that you're pushing the speed envelope of that hull a bit too much. But I'm not a cat expert, so I'd suggest you to contact Alik for that part of your inquiry.

As for this part:

And once the design is finalized, what is the best way of getting the data out of free!ship for the bulkhead shapes at each station so that i can start building it?
your best bet is to export the project to dxf file and then edit it with a 2D drafting sofware, like AutoCAD (costly) or DraftSight (free - http://www.3ds.com/products/draftsight/download-draftsight/) . Rhino can read dxf files too, if you have access to that software.
Another option is to export offsets of the stations in a txt file, if you prefer numerical output.

Cheers

[groper]

Ok here is another version... this time ive been inspired a bit more by the sailing racing cats...

http://i439.photobucket.com/albums/qq120/gravitygroper/nicks-hulls-highCP.jpg

rocker is flatter,
Cp is higher from a fuller stern,
draft is shallower,
beam length ratio has increased to a tad over 16:1 and Ive shaped the hull so that when ship is light (1800kgs) Cp = 0.61. When its heavy (2500kgs) cP = 0.64.
Center of bouyancy is 70% towards stern as most weight will be quite aft (outboards, fuel, batteries, people when fishing etc)

Ideally im looking to keep power under 60hp per side as the outboards jump up considerably in weight above this horsepower...

Do you think this would work better?

This 'Supercat' is the closest thing i can find to the type of boat im trying to design...http://www.supercat.co.za/STAMPEDE%20(4).jpg

its 11.5m X 4.8m and is powered by 2x 85-100hp for 1lt/NM @ 17kts... main differences is mine will be 10m x 3.5m and powered by 2x60hp, hoping for the same cruising speeds... Supercat in south africa also makes a 9m x 3.6m and still achieves 17kts cruises with 2 x 40hp outboards... so i know its possible, just need to get it right...

[Brian@BNE]

The old Malcolm Tennant article is worth a read, and his CS hulls with a chine and additional bouyancy aft look pretty good. This ties in to your concerns for 'hobby-horsing'. Your design likely has adequate l/b, but your challenge will be keeping weight down given your 3.5m beam limit and the limited volume in the hulls to support it.
http://www.catamarans.com/news/2006/04/CatComparison.asp

Here's an interesting alternative I saw on the hard at Sanctuary Cove show recently. Its a trailerable cat that has slide out hulls, alternative modules can be fitted on top.
http://www.getawayconcepts.com.au/trailerable-houseboats

[Richard Woods]

I thought your first sketch hull had too low a Cp, so glad to see you've increased it. I still think it could be a bit higher if you want speeds in the mid teens

It's looking a bit like my Skoota 36 powercat except that my design has hard chine hulls. I wouldn't worry about transom immersion. Check out the data for warships, lots available on line and they have similar proportioned hulls.

I assume you already have a pretty comprehensive and finalised GA. Otherwise drawing a detailed lines plan is premature

See the powercat page of my website for details of my ideas.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[groper]

Thanks Richard, ive finally managed to get michlet working now - the export file from freeship was garbage and needed a few fixes to get it working - so now i can run simulations on the different hull forms and at least be able to compare the changes in some sort of quantifiable way... interestingly, the higher Cp hulls ive modelled above 0.64 seem to get worse in total resistance... do you have any suggestions?

What do you mean by "comprehensive and finalized GA"? im not familiar with this abreviation...

So far according to michlet, this has been the best shape ive modelled so far;
http://i439.photobucket.com/albums/qq120/gravitygroper/nicks-hulls-2.jpg

Cp = 0.57
displacement = 1.215 tonnes per hull.
beam/length = 14:1
total resistance for 2 hulls = 4.08kN @ 25kts and ~2kN @ 17kts

As i suspected, michlet predicts little to zero wave interference from the closely spaced hulls above 15kts speed... maximum intereference occurs around 8-10kts...

Still a work in progress, many more shapes to try and improve on this...

[groper]

Well after experimenting with many different shapes and running them thru michlet, i came across this paper --> http://www.patentgenius.com/patent/4079688.html

So i punched in the shape as per the dimensions in the patent and ran it again thru michlet... sure enough it came out with the lowest resistence yet, although only a few percent on my best efforts thus far.

http://i439.photobucket.com/albums/qq120/gravitygroper/patent-design2.jpg
http://i439.photobucket.com/albums/qq120/gravitygroper/patent-design3.jpg

Rt = 3.8kN @ 25kts and 1.9kN @ 15kts - 2.5m hull separation center to center, gives me 3.5m ship beam overall.
Total displacement (2 hulls) = 2.43 tonnes.
Max wave height at speed = 0.19m

Length/beam ratio = 16:1
draft = .365mm
Entrance angle = 3.4 degrees

There appears to be other benefits of this shape also including a very full stern - high Cp = 0.646 for better pitch stability, and a very aft CoB at 70% which suits the loading of the vessel nicely.

Ive run GODZILLA with constraints set suitably for this design criteria and the best minimum resistance shapes it could calculate were virtually the same total resistances as the above shape, so no gains to be had according to GODZILLA whether Wigley hull form or kayak shapes modeled. So without any real resistance gains to be had, i think ill stick with this form for its better seakeeping and practical use benefits. Godzilla predicted the wave interference to be non existant above 10kts and the ideal hull separation to be pretty damn close to what i had already. 2.5m separation is about right for this set of constraints.

So I think im about done with this hull form design unless i find something else interesting... does anyone know how to calculate the horsepower required for the speed and resistances quoted above?

[terhohalme]

I dont think that Michlet (as good as it is) is very suitable for so a high froude number.

[terhohalme]

You could use Godzilla optimization for hullform with dry transom area?

[Richard Woods]

A GA is the general Arrangement drawing. Basically a sketch of the whole boat

It is drawn long before a lines plan because, for example, the centre of gravity of the boat must line up with the centre of buoyancy of the hull. Otherwise it won't float level.

It is possible, but unlikely, that the three hulls you have shown all have the same LCB. If the LCB position has changed you'll have to redraw your boat interior, deck layout etc to match the new position.

And obviously any interior features will be affected by the hull beam, which has varied in your three hulls. And you need to have an idea of the boats weight to tell you how much displacement to give it.

Design is a long spiral, don't concentrate to much on one feature at any one time

I see no reason why a light 10m catamaran powered by twin 60hp outboards shouldn't do speeds in the high teens. Once you know the drag at each speed its easy to calculate the power required.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[groper]

terhohhalme - ive run godzilla with dry transom area, there was no improvement to be had. This shape is already a minimum resistance shape as was the claim made in the patent paper. This hull ive settled on also has a dry transom, its *just* above the waterline... with a bit of squat it may run slightly immersed which im not concerned with.

Richard - i will start work on the layout now that i *think* i have a hull which will suit the layout, CoB, and loads this boat will carry based on a "best guess" thus far. Ill do some drawings of the layout in AutoCAD and post them up next time. Based on surface areas of fibreglass panels and the weight of the outboards, i *hope* i can make a decent calculation of its CoG but i think i would like help with this aswell as it seems like a problem for an experienced designer.

The layout will be quite simple and lightweight, its not going to be a block of flats... will be kind of similar to the "supercat" photo i posted earlier in the thread...

The laminate schedule will be 155kg/m3 seal primed balsa core with 600gsm d/bias glass both sides for the bulkheads (except main structural bulkheads that connect the hulls). The hull sides and bottoms will be 600gsm triax bnoth sides with an additional layer of 60gsm woven on the outside skin for minimum print/finish. - It will will be layup on a melamine table mold under vacuum (similar to the kelsall method) to make the panels, but instead using epoxy and finished with 2pk PU paint rather than gelcoat.

So the hull panels should be around 4.27kg per m^2. Then there will be some additional reinforcing along the bilge area - ill use some kevlar under glass here adding reinforcement in case i hit a submerged object... Then i need to allow for fillets and tape joins everywhere, plus the additional heavier laminate schedule for the main connecting bulkheads - ill probably incorporate some carbon if the shedule gets too heavy here. Seems alot of work to get this all worked out... any advise would be well appreciated so i dont forget anything!

Richard, what is the power required based on a total resistance of 1.9kN @ 15kts and 3.8kN @ 25kts? I dont know how to calculate this...

[Richard Woods]

Seems alot of work to get this all worked out...


That's how/why yacht designers earn their money!! ;)

Richard Woods of Woods Designs

www.sailingcatamarans.com

[groper]

Well i feel like a bit of an idiot now... it would seem that power required is as simple as;

Required Power in KW = resistance (newtons) x speed (m/s)

This gives me 14.65KW @ 15kts and 46.74KW @ 25kts.
This converts to around 20hp and 60hp respectively for the 2.4 tonne ship or half that per hull.

Of course we need to allow for losses, air resistance, non ideal reality etc etc... but it would seem that the desired speeds are very much realistic from a pair of 60hp outboards... 40-50hp motors per hull is probably about right for typical operation in the high teens and moderate engine RPM`s... anyone concur?

[groper]

well after finalizing a general arrangment and applying it to the most efficient hulls modelled in michlet, the 3D render of the boat looks like this;
http://i439.photobucket.com/albums/qq120/gravitygroper/patentdesign.jpg

I think it should be rather obvious where everything goes so i wont bother elaborating on the arrangement, unless anyone has any questions or suggestions?

The exploded view of the panels to be laid up on the melamine table look like this;
http://i439.photobucket.com/albums/qq120/gravitygroper/patentdesign_developments.jpg

Using the laminate schedule and panel areas, the shell weight = 990kgs. This does not include all the tape joins and epoxy fillets, extra reinforcing below waterline, fitout, hardware, paint etc etc although i have been a bit generous with weights on some panels to allow for this. With the 2x 60hp yamaha 4 strk outboards = 220kgs and the other non-included weight, a realistic final weight ready to sail i would expect to come in at around 1500-1700kgs. This gives me my required payload of around 1000kgs for a design displacement of 2700kgs and should give great economy with a length/beam ratio of 16:1.

Does anyone have any experience or comment on the effect of having a small run at the stern to reduce the transom area?

[Squidly-Diddly]

Click my handle and see my gallery.

As you can see, I'm just using very simple Solidworks geometry for the underwater hull shape, just to give a general idea of which is the pointy end, displacement, etc.

I'm playing with the "fits inside a 40' container box" thingy, so I'm making my hull's "hard" shape about 38'-39' because I might want a kicked up stern drive to fit inside 40'.

[groper]

Ok ive abandoned the permit trailerable width of 3.5m and taken it out to a 5m beam, therefore it will naturally live permanently in the water but allows for much more boat for very little extra shell material and build cost. Length is now 10.6m or 35ft DWL. The shell surface areas have increased from ~150m^2 upto ~190m^2.

This enabled the following GA to be decided upon;
http://i439.photobucket.com/albums/qq120/gravitygroper/GA.jpg

The arrangement is flexible and i have several options, but im already set on the saloon arrangement with galley upstairs and bathroom directly below in the hull for ease of plumbing and electrical - the kitchen and bathroom sinks, head and deckwash all lie within close proximity to the pumps, water tank and electrical system. The master stateroom lies up front with private access whilst the guests occupy the other hull. Kids bunks are an option or simply a king single forward, with a double berth aft, as shown above. This bedding arrangment has quite some scope for change however, i will decide when im building it what will work best once im standing inside the shell :)

I remain with the low cost, low maintenence, high efficiency design goal, therefore no genset is to be included (although there is room for one), energy is provided entirely by solar and LPG gas for cooking. Im estimating 500watts of panels and 400amp/hour battery bank should be enough to sustain the vessel for reasonably long periods -i say this in the sense of game fishing vacations of around 1-2weeks on the great barrier reef (where i live). The boats purpose is not intended for extended cruising for lengthy periods and its smaller size kinda precludes from this larger class of cruising yacht which i would save for 40ft or more...

Propulsion is to be via the new yamaha F70 outboards for their high power to weight ratio, 996cc engine each weighing 118kgs. Im also considering the suzuki DF90`s for an added weight penalty - 150+kgs each and a few extra knots of speed. Alternator charging increases from 17amps to 25amps also. Production designs similar to this have already proven top speeds in the order of 22-23kts from the DF90 outboards, with great efficiency cruising around 16-17kts - This is with a rather stout 4500kgs dry weight. The full foam epoxy construction im using should be much lighter than the aforementioned Polyester/gelcoat molded boats and i expect the same performance from the 70hp motors considering an estimated 1-1.5tonne lesser displacement.

In the above drawing, the main connective beam construction shown in green, is an integral part of the shell. 2 main box beams are planned with a central bulkhead beam at the rear of the saloon. The stateroom queen berth lies inside the center of the main box beam which is formed by 2 bulkhead beams as webs, and the bridgedeck and topdeck as top/bottom tension/compression flanges. The dimensions of this space, means i effectively have a box beam 1.2x1.4x5m internal, and should provide exceptional stiffness and strength. The laminate in this area will include extensive use of unidirectional fiber. The rear beam is typical of most modern backbeam designs although a larger than normal arc is provided to increase the rear deck area. It could be formed into a seat etc, however im going to keep it simple and simply maximize the fishing space.

Bridgedeck stiffness is enhanced by the structural furniture located central, the rear saloon bulkhead frame, and a single longitudinal glass stringer running between the 2 main beams along the underside of the bridgedeck (which isnt shown in the drawing)

I have considered small diesels such as the cummins 1.9L TDI @ 75kw etc. The weight is around 200kgs each, higher initial cost, more difficult maintenence and engineering means its hard to justify for a small increase in fuel efficiency... Im not even going to attempt to work out how many sea miles id have to cover just to recover the higher initial cost alone, suffice to say it would be several circumnavigations of the globe...
Heres an unfinished rendering showing the lines;
http://i439.photobucket.com/albums/qq120/gravitygroper/patentdesignwide1.jpg

Does anyone have any suggestions? im selling my car to pay for materials to build this, and i expect to start building shortly...

[sabahcat]

Looks suspiciously like

http://cdn.cruisersforum.com/forums/attachment.php?attachmentid=35061&d=1324638380

http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-127.html#post510685

[FAST FRED]

"400amp/hour battery bank "

Does this assume the batt bank will be only discharged by 50% for long service life?

Cruisers seldom get to 100% full SOC , so most will size a batt bank to be sufficient between 50% and 85%.

FF

[groper]

hmm, good call on the electrical system, i had not put much thought into this yet as i figured id work it out later and size the batteries accordingly... in the latitude i live we get 6.1 hours of the full rated solar capacity installed. Therefore, with 500watts of installed panels, i should be able to generate 3 kw/h per day assuming clear weather + whatever charge is added by the outboard alternators - which id estimate running for around 3hrs per day at cruising speed whilst at sea, some days would see upto 8hrs per day when trolling for pelagic fish etc. The F70 outboard alternators are rated @ 17amps @ WOT each but i have no idea what is the actual charge current generated on an average daily usage basis?

The main consumer of electricity will be refrigeration/freezer. Everything else has a negligible power consumption such as the LED lights, and GPS etc... the depth sounder would be the next biggest consumer, but i only run that whilst the engines are running typically so im going to ignore this for now. There will be no air conditioning and for hot water i plan on using instantaneous LPG system - which is also used for the hotplate burners and BBQ. So, the planned freezer space is 150L and the food/drink fridge will be around 60-80L in capacity. There will also be large underfloor insulated boxs for whole fish etc and large amounts of beer will be kept in here prechilled with block ice in PET bottles before departure. From experience i can get around 5 days from this before the beer has gone too warm to be enjoyable and needs to find a fridge etc and the frozen bottles become drinking/cooking water... same goes for the freezer, fill it with frozen things first... the idea is to take as much stored energy with you as possible before unpluggin the shore power...

That said, whats a fair energy consumption figure of a 150L freezer and an 80L fridge, assuming its well insulated with 3inch foam? I have the current draw specs on the compressors but the actual consumption per day is too variable to make a calculation, id simply ask those with experience to chime in here... but at the end of the day, i can always add another battery or 2 if i find my energy needs are not being met - i cant stand the noise of wind generators and engine generators running however, i will put more panels and batteries in if i have to, whatever it takes to avoid that damn noise.... one of the best things i enjoy when going away is the peace and quiet of a secluded anchorage, leeward a rainforest covered island beach on the great barrier reef with the smells of the days catch cooking on the BBQ wofting across the deck with beer in hand... :)
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/228219_6158375405_730960405_237515_3256_n.jpghttp://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc6/227034_6158380405_730960405_237516_3589_n.jpg

I was under the impression AGM batteries could be run down as low as 30% of their capacity without damage?

[groper]

an updated GA and profile;
http://i439.photobucket.com/albums/qq120/gravitygroper/untitled.jpg

Everything has been moved aft 700mm as im worried about having enough bridgedeck clearance at the front of the tunnel due to the fine bows... does anyone know a good method for determining this clearance with respect to forward reserve bouyancy and speed?

Now everything has moved aft, its looking a little bum heavy... although the hulls have a CoB at 40%, the masses are still quite aft, i may have to extend the transoms to get more bouyancy at the stern...

[Richard Woods]

You may find it is better to have a more gradual slope to the forward part of the bridgedeck. Many multihulls are too vertical fronted.

If you really mean your CofB is 40% aft from the bow then it is almost certainly too far forward for any boat, but especially for a powerboat

I guess you saw these comments on the FAQs page of my website

"Recently "ram bows", or a reverse rake, have become popular on beach cats and of course now feature on the new America Cup boats. They are even seen on some cruising multihulls.

I'm not sure about that though, it seems impractical to me. I have often had times when I've been anchored in light winds and when the tide changed have had the anchor line catch under the stem. Obviously with a ram bow the warp will not release itself under the hull but rather ride up to deck level.

At the very least this will be noisy and disconcerting, especially if you are asleep at the time. And I'm not sure what happens when hitting flotsam or weed, while coming bows-on into a dock or to another boat is tricky if you cannot fend off easily and safely. (And any damage will be on the WL not high up)"

Richard Woods of Woods Designs

www.sailingcatamarans.com

[groper]

No, its 40% from the stern, so 60% from the bow... probably not the way a NA is supposed to dimension things, but then again, im certainly no naval achitect...

Ive read your blurb on "ram bows" and i agree with nearly all of it... What i have been trying to acheive is basically a plumb bow, with a tiny bit of aft rake for aesthetics... there is only 200mm of rake from the forward vertical to deck level. According to the cross section areas, the bows should be virtually the same volume as a plumb bow of similar dimensions. The 200mm has been "added on" rather than subtracted, so there should actually be slightly more volume in them compared to say a 10.4m boat with plum bows etc... I think it would also be easier to build ram bows with a very fine entry on the waterline compared with other designs... i beleive this helps lower resistance with a very low entrance angle.

Still, im wondering how to best determine the forward bridgedeck transition location in order to maximize volume in the boat?

My best reckoning is putting it about 32% from the bow at 750mm above waterline assuming zero angle trim, hows that sound?

[groper]

BTW, the underwater hull shape ive designed is very similar to this one;
http://www.boatdesign.net/forums/attachments/boat-design/40354d1265251993-wave-piercing-experience-incat-rocks.jpg

Its different to the usual displacement shapes, primarily designed for operating at high froude number... Im hoping i can cruise at a froude number around 1.0 without burning TOO much fuel...

[masrapido]

Hmmm... Am I the only one that cannot see the underside of the hull on the photo...?

[groper]

The INCAT shown above, is built from aluminium plates, and so has chines... but its similar in form to this with one key difference;

http://static.guim.co.uk/sys-images/Sport/Pix/columnists/2009/9/1/1251815843670/alinghi-5-001.jpg

The fullness of the midbody aft does not taper off to a thinner and shallower section- because its a powerboat rather than a sailboat and we dont want it to squat. Sailboats have the opposite problem of course, so they remove some bouyancy from the stern. Its an interesting form whereby the front 1/3 bow section produces a wave that partially cancels the wake of the midbody and lowers the overall wave making resistance.

[groper]

This rendering shows the shape better...
http://i439.photobucket.com/albums/qq120/gravitygroper/hull.jpg

And this is the 3D rendering of the boat as its currently dimensioned in the 2D autocad general arrangement i posted previously;
http://i439.photobucket.com/albums/qq120/gravitygroper/escape35.jpg

I think im about ready to start cutting some frames...

[Mr Efficiency]

So you've gone from a transom clear of the water to a deeply submerged transom ? This could restrict your efficient speed range, no ? Don't cut those frames just yet !

[Mr Efficiency]

Also, there is an issue with outboards on a deeply submerged cat transom as regards keeping the powerheads far enough out of the water, particularly the h.p. range you are talking, with 20" legs as long as you can get. At the other extreme, with a transom just kissing the waterline, you have the problem of running the cav plates well below the bottom to stay in solid water, with a marked increase in drag.

[groper]

Hmm, nicely spotted mate, thanks for the consideration - ill have to look into this more closely...

The designed displacement of this boat as it sits at this point in time is 3500kgs. At this displacement, the waterline is 400mm from the keel. If i sink it further down on its lines to 450mm, it displaces 4150kgs - which i would call its maximum displacement when overloaded as the bridgedeck clearance would then be reduced to 700mm.

According to the yamaha specs, they reccommend a transom height of 508mm, this puts the cav plate 1 inch below the transom bottom. http://www.yamaha-motor.eu/uk/binary/F70%20uk_Leaflet_tcm230-414389.pdf

So as it sits at 3500kgs, the transom top where the outboard bracket bolts onto would be 108mm clear of the waterline at rest. Underway, backing down on a fish, i wouldnt be comforatable with this, probably drown the powerheads when reversing into the wind... damn, i might have to change things to look more like the americas cup hulls and see if i cant get another 100mm... or just bite the bullet and put 25in shaft 90hp 4 strks instead... :(

[masalai]

Why this interest in an "axbow bow"? - That does not add to displacement efficiency apart from making the LWL a little longer than the LOD? WTF for?

Chamberlin C10 uses a pair of 50HP diesels, a horizontal shaft, gives better than 15 knots and at that speed is somewhere around 1 NMile / litre... It has done extended passages and is one I should have bought (everyone is wise in hindsight)...

[Mr Efficiency]

Hmm, nicely spotted mate, thanks for the consideration - ill have to look into this more closely...

The designed displacement of this boat as it sits at this point in time is 3500kgs. At this displacement, the waterline is 400mm from the keel. If i sink it further down on its lines to 450mm, it displaces 4150kgs - which i would call its maximum displacement when overloaded as the bridgedeck clearance would then be reduced to 700mm.

According to the yamaha specs, they reccommend a transom height of 508mm, this puts the cav plate 1 inch below the transom bottom. http://www.yamaha-motor.eu/uk/binary/F70%20uk_Leaflet_tcm230-414389.pdf

So as it sits at 3500kgs, the transom top where the outboard bracket bolts onto would be 108mm clear of the waterline at rest. Underway, backing down on a fish, i wouldnt be comforatable with this, probably drown the powerheads when reversing into the wind... damn, i might have to change things to look more like the americas cup hulls and see if i cant get another 100mm... or just bite the bullet and put 25in shaft 90hp 4 strks instead... :(

It's a shame they don't make them for 25" in the smaller sizes, however at one stage you could get factory extension kits for some motors in that 50-70 hp range, and maybe still can. Someone may have experience with that, but motor drowning is an issue with cats, made more problematical by the motor sitting right out there on the corners, combined with the skinny sponsons.

[groper]

I can already see where this is heading... im going to have to put 90hp outboards on it...

This isnt such a bad thing tho really, the engines wont be working as hard for a given cruise speed and i doubt the fuel economy would change much, if at all, using the larger engines as they would probably end up in a more efficient rpm range for my desired 20kt cruise speed. The only penalty is 50kgs per engine and a couple thousand dollars on the purchase price, im happy with that...

[Mr Efficiency]

I can already see where this is heading... im going to have to put 90hp outboards on it...

This isnt such a bad thing tho really, the engines wont be working as hard for a given cruise speed and i doubt the fuel economy would change much, if at all, using the larger engines as they would probably end up in a more efficient rpm range for my desired 20kt cruise speed. The only penalty is 50kgs per engine and a couple thousand dollars on the purchase price, im happy with that...

20 knots cruise sounds a bit optimistic, I think too, you have to be mindful of the gear ratio and the higher reduction ratios and bigger prop diameters are preferable for your likely cruise speeds. Varies a bit between engine makes.

[Richard Woods]

20 knots with twin 90's should be quite feasible.

Here is a photo of my 35ft Banshee catamaran towing a waterskier at 22 knots with twin 90hp. We had earlier sailed this boat at 19 knots. Sorry for the quality, it was taken over 20 years ago.

This is a 26 year old design and obviously is primarily a sailing boat. So it has a sailboat hull, hence the extreme trim. Removing the rig, keels and rudders would increase speed some. Speed would increase significantly with a hull designed as a powerboat only

Richard Woods of Woods Designs

www.sailingcatamarans.com

[groper]

HAHA, thats gold richard! i love it... can imagine all the bewildered looks you received from people you passed by that day... classic...

I think 20kts is perfectly realisitc aswell, ive been known for being a bit of a risk taker, and ive not published by plannned laminate shedule as yet... the empty weight of the boat splashed including engines should come in well under 2.5tonnes... using the 190m ^2 of panel area in the shell and structural furniture and the correct densities of each panel, im only upto 1500kgs...

Iill likely use carbon in key structural areas, ie beams... using twin 90hp instead of the original planned 60-70hp, i should have a displacement catamaran with one of the highest power to weight ratios in recent times i would think?

[groper]

One more thing, ive been thinking about the electrical system some more... the weight of all those panels and batteries and accociated fixings/wiring etc adds up to quite some weight... Im thinking a little honda 2Kva genny, mounted below deck with some sort of ventilation might be a better answer. I have unleaded fuel in the tanks anyway, run a fuel line directly to it... So only need the 2 semi deep cycle batteries for starting engines and running the fridges overnight. End up much lighter and cheaper... anyone done this before?

[Mr Efficiency]

Another thing to consider is whether your tilted outboards clear the water when the boat is moored. Not desirable to be growing barnacles inside the water intakes.

[masrapido]

The more I'm looking at the hull, the less I am convinced it is a good choice of shape ... Way too much surface, square end submerged and not a planning shape to bring the rear end out of the water, not even close to the surface... It'll create a huge hole behind it, and a huge drag. It will plough through the water.

[groper]

The shape is based on a minimum resistance high speed displacement hull form described in a patent from 1978. Relevant points i have extracted below;
http://i439.photobucket.com/albums/qq120/gravitygroper/chart-1.jpg
http://i439.photobucket.com/albums/qq120/gravitygroper/patentextract.jpg

[Mr Efficiency]

Groper, for your information, there is a high thrust 4 stroke 60hp Yamaha with XL shaft according to 2011 catalogue.

[groper]

Thx Mr E, but I cant find it, do you have a link?

[Mr Efficiency]

That was from a printed catalogue of Yamaha 2011 series outboards, engine model FT60DETX. Transom height is quoted as 25.4". Seems it is still current.......

http://www.yamaha-motor.com.au/products/marine-outboard/4-stroke-mid-power/10-ft60d
click on "Specifications" to see the two shaft length options.

[groper]

well geesus, wouldnt ya know it... it also lists the F70A with XL shaft and 2.33:1 gear ratio now too... looks like im back to 70hp outboards again :)

[groper]

Been doing some seakeeping analysis as i was worried about bridgedeck clearance with the fine bows im using... seems it should be ok. Heres a simulation @ 20kts boat speed of a randomized wave spectra on a 4m swell. Heading is 45deg from head seas to show roll characteristics aswell.

ugN7LAxjm0A

[Willallison]

Just had a quick skim through this thread, so if I've missed something, I apologise, but from what I've read, you seem to have put a whole lot of horses before the cart...
1st off, I don't think it is feasible to build a durable 35ft cruising cat that weighs in at around 2500kg. Obviously, you need to do a thorough, detailed weight estimate before you can even begin to think about things like powerplants etc. As a starting point, you ought to at least look at some published displacement figures from other similar boats. Ideally, you want to know the as built weight, though this tends to be hard to come by... Perhaps Mas can tell us the weight of that Chamberlain, for instance...

[groper]

Well, ive got a reasonably accurate shell weight including the 2 outboards which i added to the transom weight (highlighted in the pic below, weights are in tonnes so remove the decimal and you have Kilograms)

To this i need to add;
a few more small composite panels and stringers, internal furniture etc here and there which i havnt bothered drawing, done in 40kg/m3 foam with thin laminate;
then probably 20kg of paint;
then fitout inc all electrical, honda 2kva inverter, 60l fridge and 150l freezer, 2x batteries, hydraulic steering, cleats, ground tackle, mattresses and upolstery; toilet, head, pumps and water;
the fuel tanks are built into the composite structure already;
Id like to put down some 10mm teak strip plank decking in the saloon and on the back deck - which is gonna cost me about 100kgs, but i like the look so...
A bunch more other bits and peices, but thats the main bulk of it taken care of...

i reckon i can bring in all this under 500kgs comfortably, which means i have a lightship displacement of just over 2 tonnes...just add people, fuel and im fishin...

Most boats are built stronger and heavier than they really need to be, and until recently most boats used inferior composite sandwich materials or no sandwich structure at all - so needs to be much heavier for the same strength and stiffness. So one needs to be careful when making comparisons or assumptions of weight based on what looks to be a similar type of boat, you cant tell by exterior appearance whats really inside of it... it could be a lead sled (over engineered, chopper gun sprayed polyester solid skin boat) or a rocket ship (well engineered, PVC foam cored, glass/carbon/epoxy sandwich boat)

[sabahcat]

Id like to put down some 10mm teak strip plank decking in the saloon and on the back deck - which is gonna cost me about 100kgs,
Why 10mm and why teak?
Have used 5 before with no issue and there are other products http://www.yachtdeck.com/

[groper]

Hmm, didnt know this stuff existed... thanks for the heads up on flexiteek... i definately look into it...

[Willallison]

The weight estimate for a boat like that - if it's prepared properly - will run to several pages in length. And whilst I agree that many boats are over-built, there are also a number that are marginal at best. The Chamberlain that Mas posted is designed by a very highly respected designer whose boats are probably at the lighter end of the properly engineered spectrum.
And for every home-built boat that floats on its marks when launched there are probably a hundred that are far heavier than they were expected to be.
Yes... a proper weight estimate is a lot of work. But a whole lot less drama than a boat that is too heavy.
Just my bit of advice... you can take it or leave it....

As far as synthetic teak goes, there are (IMHE) only two worth considering.... Esthec ("plastic") and Marinedeck 2000 (cork). I put the latter throughout my own boat (http://imaginocean.net/contents/en-us/d8.html) and am very pleased with it....

[tunnels]

Why are boat getting more and more ugly as time goes by :eek:
They used to be things of great beauty but seems we have lost all respect for beautiful thngs , the more ugly the more people rave over them ! sorry !!i i was looking to make a new boat and a designer presented me with drawings for one of these hidious looking things i would toss him out on his ear and tell him to go back to kindy !

[Alik]

The weight estimate for a boat like that - if it's prepared properly - will run to several pages in length. And whilst I agree that many boats are over-built, there are also a number that are marginal at best.
...


There is another reason - poor weight control. Builder/Customer keep adding without looking at table of weights... Well, on MY boat difference in design weight and actual weight was 4kg :)

Meanwhile, may times when we see attractive specs for some Australian-designed cats we need to realize there are no option such as genset, air-conditioning, teak etc. included. At leas I try to design fair boat and put fair weight in specs, also structure in compliance with ISO12215-5.

[daiquiri]

Why are boat getting more and more ugly as time goes by :eek:

Same for buildings, imho. There are plenty of beautiful ancient and old buildings in (for example) European cities which inspire a sense of deep admiration and respect for architects and artisans who have designed and built it. A care for details can be felt by looking at every single stone, brick or a piece of metal they are built of. The 18th century was particularly generous in that sense.

Today we have these giant cubicles made of glass, steel and concrete which inspire nothing to those who are observing them. Buildings with no soul, designed just for quick construction at minimum cost. Guess they're a perfect reflection of the times we are living in, ruled almost exclusively by God of money. :o

[groper]

sorry tunnels, i use several different softwares to model the boat and at this time, its easier for me to use the freeship software with respect to the panel areas and weights shown above... the proper rendering (shown in white) was done a page back in the thread... if you still dont like it, then thats your perogative, i have designed what i like - for my eyes...

One thing needs to be remembered about this boat - its not a cruiser or liveaboard... its a lightweight sports fishing boat with minimal "creature comforts". Typical use will be day fishing trips and the occational "weekender" type trips, all within the partially smooth waters of the barrier reef...hence the need for speed due to limited time on the water. The interior will be very minimalistic and simplistic... no air cons or TV`s, no diesel gensets, nothing that doesnt need to be there etc... this is not a luxury boat...

[daiquiri]

Groper, I would be interested to learn how did you create frames and bulkheads with the freeship? To avoid the side-drifts in this thread, you could reply here (if you wish): http://www.boatdesign.net/forums/design-software/creating-frames-stringers-concentrated-masses-etc-freeship-delftship-38103.html
Cheers

[Richard Woods]

Years ago I was involved with one boat built from light weight panels and the joints weighed more than the panels

Boats are usually heavier than you hope (and more expensive, and more time consuming). In any event never lighter/cheaper/quicker

Having said all that, a simple 35ft boat ex fuel and with light engines can weigh 2.5T built in foam sandwich

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Richard Woods]

Heading is 45deg from head seas to show roll characteristics as well.

Motoring into swells at 45deg is usually the best (ie least motion) option. Head on, or beam to, seas is usually a worse case

Richard Woods of Woods Designs

www.sailingcatamarans.com

[sabahcat]

As far as synthetic teak goes, there are (IMHE) only two worth considering.... Esthec ("plastic") and Marinedeck 2000 (cork). I put the latter throughout my own boat (http://imaginocean.net/contents/en-us/d8.html) and am very pleased with it....
Yes, thats the one I was looking for.
Not cheap, but neither is a laid deck.

[groper]

Years ago I was involved with one boat built from light weight panels and the joints weighed more than the panels

Boats are usually heavier than you hope (and more expensive, and more time consuming). In any event never lighter/cheaper/quicker

Having said all that, a simple 35ft boat ex fuel and with light engines can weigh 2.5T built in foam sandwich

Richard Woods of Woods Designs

www.sailingcatamarans.com

I agree, which is why the designed displacement @ DWL, loaded and ready to sail is 3.5 tonnes... 2.5tonnes is the lightship displacement...

For those that havnt read the entire thread, the design has evolved and changed over the course of the thread...

[Willallison]

As I said... I hope you will take my input in the manner iin which it is intended... I'm not having a shot at you.... just trying to be of assistance - that is afterall why you posted, isn't it?

I haven't had time to look over your short weight table in any real detail, but let's just look at two points:

1. You show the glazing as being 10mm thick all around. The required thickness is determined by material type, minimum spans and area of operations. The sides can usually be somewhat thinner than the fronts. But that aside... The density of Lexan is 1200 kg/m^3 - so 10mm thick will weigh 12 kg/m^2. The density of glass is approx 2500 kg/m^3, so will weigh 25 kg/m^2. Your weight table shows it at 6kg /m^2.....

2. It is unusual to see 40 kg/m^3 foam used as a structural core... 80 is the most commonly used. This varies of course, depending on the application and the engineering involved. Such low density foam will be more prone to damage from impact, so will compromise your desire for thin FRP skins. 13mm looks at 1st glance to be optomistically thin too... particularly for the hull shell and definitley for the decks. Such thin panels will require quite a bit of support (internal framing). I don't know how much experience you have in engineering a structure like this (you may have plenty...) - and there certainly isn't anywhere near enough detail in the images you've posted to make an educated guess, but if you are approaching this as an amateur, can I suggest that you at least go to the small expense of getting it checked by someone with the relevant knowledge and experience... it'll definitely save you money, time and heartache in the long run....

As to the looks... beauty is in the eye of the beholder as they say.... I reckon it looks a whole lot better than any number of boats I see out there - both proffessionally and amateur designed.... but then again I like steel and glass cubes...:P

[groper]

This boat has a claimed lightship displacement around 3 tonnes, max displacement is 5 tonnes, and its fitted with a pair of 100hp yamahas... gets along quite well too;
sJ7xwaUJCs0

[Richard Woods]

But surely that's an open deck boat with no interior??

Richard Woods of Woods Designs

www.sailingcatamarans.com

[IMP-ish]

What is the Supercat 38's WOT speed with the 100 obs?

[groper]

They claim WOT speed is 27kts...

Richard, yep theres bugger all accom in the hulls, couple single bunks and the like.. Again, its a fishing boat, not a liveaboard cruiser... I plan to keep my boat along the same lines -very minimalistic, nothing but bunks and a very small bathroom (which will never get used) to keep the admiral happy. The Admiral is a land lubber and always will be... My design does not have an enclosed saloon either, its open to the back deck... i considered the clear vinyl curtains idea with no real cabin structure, but the spray is always present therefore the side/front curtains always remain down so might aswell have proper windows that can be opened all done in lightweight composite. Id hate to think what all that stainless flybridge structure weighs, not to mention the cost...

[Mr Efficiency]

Here's a pretty impressive vessel, bigger than the subject of this thread, but it handles chop like it's not there. There is a lines drawing of it on the website, and it has a deeply immersed transom. It is running a fair bit of power, presumably that could be scaled back somewhat.
http://www.youtube.com/watch?v=wGh2rML-41Q&feature=related

[Mat-C]

As I said... I hope you will take my input in the manner iin which it is intended... I'm not having a shot at you.... just trying to be of assistance - that is afterall why you posted, isn't it?

I haven't had time to look over your short weight table in any real detail, but let's just look at two points:

1. You show the glazing as being 10mm thick all around. The required thickness is determined by material type, minimum spans and area of operations. The sides can usually be somewhat thinner than the fronts. But that aside... The density of Lexan is 1200 kg/m^3 - so 10mm thick will weigh 12 kg/m^2. The density of glass is approx 2500 kg/m^3, so will weigh 25 kg/m^2. Your weight table shows it at 6kg /m^2.....

2. It is unusual to see 40 kg/m^3 foam used as a structural core... 80 is the most commonly used. This varies of course, depending on the application and the engineering involved. Such low density foam will be more prone to damage from impact, so will compromise your desire for thin FRP skins. 13mm looks at 1st glance to be optomistically thin too... particularly for the hull shell and definitley for the decks. Such thin panels will require quite a bit of support (internal framing). I don't know how much experience you have in engineering a structure like this (you may have plenty...) - and there certainly isn't anywhere near enough detail in the images you've posted to make an educated guess, but if you are approaching this as an amateur, can I suggest that you at least go to the small expense of getting it checked by someone with the relevant knowledge and experience... it'll definitely save you money, time and heartache in the long run....

As to the looks... beauty is in the eye of the beholder as they say.... I reckon it looks a whole lot better than any number of boats I see out there - both proffessionally and amateur designed.... but then again I like steel and glass cubes...:P

Groper - not sure if you missed this last post from Willallison.... Like you I suspect, I'm here as an interested amateur. My experience is that even though you might not like what you are hearing from a number of these guys, pretty much everything they tell you will prove to be correct (in the case of the pro's that is....)
Oh - and I rather like glass cubes too!;)

[Richard Woods]

I agree those weights imply careful design and build

But 6mm lexan would be strong enough for the windows, so say 7kg/sqm

If you use 10mm foam you are probably OK with 40kg/m3 density and you'd end up with roughly a 13mm laminate thickness total (approx 1.5mm skin each side sounds right). I'd use more on the bridgedeck bottom though and you'll find the decks will flex (disconcerting to some, even if strong enough)

But there is no margin for error and most people would only use a boat built to those scantlings inshore in flat water.

Remember, scantlings are usually higher than theoretical to allow for building errors, operator errors and to extend structural life

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Alik]

But 6mm lexan would be strong enough for the windows, so say 7kg/sqm

From calculations to ISO12216 6mm is not enough for such big windows. Actually it gives thickness few percent higher than PMMA, because also stiffness is considered.

[Willallison]

I've not run numbers to check the validity of any of the stated "scantlings"... I was just pointing out that in at least one area (the glazing) the given weights are out by 50%! It's not meant as a cheap shot at groper, I'm merely trying to reinforce the need for using realistic numbers.
But Alik is quite right... 6mm would certainly not be thick enough for the fwd facing windows.

As to the foam, again, I've not run numbers... but 10mm 40kg/m^3 foam with 2 x 1100 gsm skins (approx 3mm total thickness) certainly sounds a bit light on to me, unless you plan on having a great deal of closely spaced interior support structure and even then you face problems with the potential for puncture. This is intended to be a fishing boat. That implies offshore use and a fairly tough life to me.... I would prefer to be a little more conservative with the scantlings and be confident that that boat I was heading out in is likley to bring me home again....

[Alik]

1. We use 40kg/m3 foam for only for furniture. Likely it will not comply for sides and bottom.

2. 2x1100g/m2 skins? There is min laminate weight criteria for outside skin, it will not comply. Just for reference - for Lloys SSC rules min bottom outside skin is 4.5mm thick; similar numbers for DNV HSC. For ISO12215-5 it would be lighter but not just 1100g/m2.

[groper]

Ok guys i need to clarify some things... firstly about the panel weights in the table i posted earlier and regarding window thicknesses etc;

The way the software calculates the weights is by the thickness, density and area of the surfaces so drawn... however, when dealing with composite panels which can have different laminates applied to the core, and different core thicknesses, the density of the panel is always changing... therefore i cannot simply use the true panel thickness and density without recalculating the density everytime im using a different laminate. So, what i do in some instances, like with the windows etc, is simply change the density until i acheive the desired weight (which i calculate longhand by adding the resin/glass/foam weights per m2 of laminate) and leave the thickness alone or visa versa... So the thicknesses you see in the table are not correct and neither are some of the densities, but the panel weights should be close - provided i havnt made a mistake in my longhand calculations somewhere which is possible and is something i need to check.

There is no way im using 10mm lexan for the windows btw, way too heavy...im going to try 6mm... and there is no way the window lexan will be the size of the surfaces as shown, the window surface as shown is actually a composite panel including the windows within them, which has to hold the roof up etc... so imagine a frame around the windows dividing them up into smaller peices (which will also make them stiffer)

I dont have the tools nor expertise to model the boat 100% accurately, and i do realize the boat will be heavier than whats shown in the table i posted earlier, much heavier in fact, but i feel there is enough headroom with the designed displacement of 3500kgs. It will not be built to survey standard - its for private use only. ill get to the scantlings later in the thread...

This boat shown earlier in the thread, was just launched at around 2500kgs; it doesnt have as much beam as mine, length is 10m, built on balsa core not foam i beleive...
http://cdn.cruisersforum.com/forums/attachment.php?attachmentid=35061&d=1324638380

[groper]

Theres no way im using 40kg/m3 foam for the hull... if the original post was read correctly, its to be used in internal furniture construction and glass laminated stiffeners/stringers....

[Alik]

The way the software calculates the weights is by the thickness, density and area of the surfaces so drawn...

Not the software we use. Those ones are using weight of glass fabric, resin content, actual sore, etc. After all, we add some overweight margin to cover resin penetrated in core, some reinforcements, etc.


There is no way im using 10mm lexan for the windows btw, way too heavy...im going to try 6mm... and there is no way the window lexan will be the size of the surfaces as shown, the window surface as shown is actually a composite panel including the windows within them, which has to hold the roof up etc... so imagine a frame around the windows dividing them up into smaller peices (which will also make them stiffer)

Starting from l/b>2 only the width b effects the thickness of plate. So would You split the windows vertically also? :D


This boat shown earlier in the thread, was just launched at around 2500kgs; it doesnt have as much beam as mine, length is 10m, built on balsa core not foam i beleive...

It might be substandard design or build, or launched without some equipment, or marketing numbers, or wrong measurement... Just make real table of weights for Your boat, no need to guess.

FYI: mass of structure ms for powercats, kg:

ms=e*L*B*D

where L, B, D are hull measurements, m;
e=28…34 kg/m3 for planing catamarans in FRP; e=20…26 kg/m3 for displacement catamarans in FRP

[groper]

My initial scantlings are as follows;

Hull, cabin walls and top deck = 15mm 80kg/m3 PVC foam with 900gsm triax outside and 750gsm triax inside. Additional 600GSM Kevlar on hull bottom/bilge.

Bridgedeck = 20mm 80kg/m3 PVC foam with 1500gsm triax both sides

Beam bulkheads/webs (2 per beam) = 20mm 150kg/m3 EG.balsa with 3000gsm uni-directional both sides. Additional uni added to top and bottom beam flanges (bridgedeck and topdeck) to close the beam box.

Using these scantlings, the rough weight of the shell including 250kgs for the outboard motors comes to 1386kgs... i already added extra density in the chart i posted earlier to allow for things like tape joins and epoxy fillets etc... which is why it came out around 1500kgs.... ill post a new panel weight chart soon, but i gotta run to work now... the original chart had different thicknesses as it was originally going to be built from 12mm balsa core instead of 15mm PVC foam...

Do these sound like realistic scantlings, or am i still dreaming?

[Alik]

My initial scantlings are as follows
...

What is the basis for Your scantlings?

[harry cassin]

Glad to see you designing you own cat, i wish i had enough knowledge to be able to work cad etc, I was going to do a 50 foot simpson some years ago and thought on it for 6 months and came to the realisation that it's a huge commitment.

[groper]

And so it has begun...



These are the first 2 peices of this boat to be infused;
http://i439.photobucket.com/albums/qq120/gravitygroper/20120415_180433.jpg



They are 2 of the webs in the forward beam which will also form the sides to the anchor locker etc...

All bulkheads and beams have been cut out of the airex foam sheets via CNC router from the CAD drawings, the files sent to the local CNC guy look like this;

http://i439.photobucket.com/albums/qq120/gravitygroper/bulkheads.jpg



Ive put together the mold for the hull "shoes" and this will be an interesting experiment to see how well a direct female mold for infusion works... its built very lightly out of 3mm foamed PVC as an inside former, with a skin coat of glass/epoxy to seal up the joins and staples etc... i have no idea how well its going to work with infusion, could be a complete disaster and destroy itself or a surprising success!

http://i439.photobucket.com/albums/qq120/gravitygroper/20120407_160844.jpg

Here is an updated rendering of the boat as ive made a few changes prior to finally making up my mind :D

http://i439.photobucket.com/albums/qq120/gravitygroper/newstern.jpg

The weather is absolutely atrocious these last few days, so i cant do anything outside, but I will be gradually getting thru things over the next few months when the weather improves... just doing some more small infusions to get a better feel for how things work, then ill go for those hull shoes! So far so good... happy days :D

[harry cassin]

Looks fantastic, hope to see many more photo's

[groper]

Busy infusing bulkheads lately... ive worked out that its quicker and easier to hand laminate small panels, its only worth infusing the larger panels IMHO... so im planning the infusions to be as large as possible from now on...

So heres a few pics;

This is a few peices i hand laminated on the table;
http://i439.photobucket.com/albums/qq120/gravitygroper/Boat%20Build/20120501_084056.jpg

Heres a pic showing how im doing the cutout reinforcement in the bulkheads. The cutout is routed out of the foam core, then fill the bottom of the channel with thickened epoxy and let it setup. Then wetout some 1000gsm UNI tape, fold it up and push it into the channel and finish it flush with some more thickened epoxy. Once its all cured, i infused the top and bottom skins over this, and trim it back to the solid UNI edge once cured. You could do all manner of cutouts like this, windows, doorways etc...
http://i439.photobucket.com/albums/qq120/gravitygroper/Boat%20Build/20120510_173218.jpg

And this is the end of the infusion of one of the beam bulkheads including the shear web reinforcement, aswell as the 6mm x 100mm thick solid UNI top and bottom caps rebated into the foam and infused in 1 shot after the cutout reinforcement. This panel is 5m beam * 2.2m depth to give an idea of size and weighs 38 kilograms + whatever paint goes on later. Will do another one of these tomorrow if all goes to plan :)

http://i439.photobucket.com/albums/qq120/gravitygroper/Boat%20Build/20120511_175821.jpg

Happy days...