Trailerable Multihulls

Point taken... I stand corrected and appropriately chastened...

 

No apology needed

Darn internet - no need for chastity - you can tell I am no priest. The thing about a good thread is that it doesn't descend into name calling. I hope you don't feel like I was.

I do like John's rig. I never got to sail on his new boat but I did get to look over Wired a few times. That boat was incredibly interesting to me. I hope she is re-built now after being hit by lightning.

John has extreme cred when he does something "strange". He was the co-designer (along with Lock Crowther) of the Kraken 33. He built that (Manta 2) to replace his Bandersnatch which capsized (killing 4 crew including Lock's brother - boat broke up dead whale nearby -it won the only Sydney to Hobart for multis -1966) Manta 2 won heaops or races a set a great record to Gladstone. He then built a large Crowther cat for cruising - Hitchhiker and then Wired. Now his new boat.

His ideas (especially his engineering ideas) demand very close consideration for offshore sailing. His use of tension wires and compression struts rather than simply supported beams allowed him to make Wired beamy and very light while still being incredibly stiff. Robin Chamberlin, designer of my Kankama, used a similar arrangement on his Antarctic cat Excess.

I will tell you more about my little rig idea. I have a skiff mast on Cats-paw. 9 metres long and 1 kg/m section. The thing threatens to fall down all the time. The proper section for the cat is 2.2kg/m. This will make lifting it a struggle. On the 7 I have a 10m mast which the rig designers say has to be 3 kg/m bare section. This needs 5m x 30kg = 150kgm to rotate up.

But if you cut the top 1/4 off the mast you get a mast that weighs 22kg with a centre of gravity 3.75m up. Instead of 150kg/m to raise the mast you only need 82 kgm to raise it. Almost half.

Then you have a carbon spar arranged on the sail like a laser mast for the top mast. It slides up the mast on an RCB car (a headboard one). At anchor you get a little less windage and when reefed less pitching.

On of the main reasons for getting the mast lighter and lower is that I would like to have it up when folded. It gets a little scary with a raised mast when folded so lowering the CG is a real boon.

cheers

Phil Thompson

 

Not at all Phil, just look at the mix of my posts... vainly trying to be a "reformed masalai" yet still the "pontificating prick" bursts onto uninvited scenes - - and look at my new avatar - the pure innocence of a ten year old me

Nice idea but for an oldie like me - averse to lifting heavier than a wine glass full, gives me a feeling of "better you sire"... Even so would appreciate your presenting the idea for perusal on this net... The biggest sail to drop in my proposed rig is the blade/storm trisail. the other 4 are all roll-up... Nothing else except a couple of "spinnaker poles" to push sails out in dead downwind...

 

Hello Masalai,

I think I remember reading something on that set-up. My forte is not at the power source and it may be that I'm wrong, but if I'm looking at the layout correctly, it may not be a good choice for the design. It looks like it is really hard to tack and that could be a big no no in close quarters or close encounters.

Eventually, I guess I will need to give serious thought to the type of rig for the design because it will have to be lighfooted on tack. Again...not my forte.

Thanks
J

 

Unless they are hardened monohullers that look for the doldrums just to get becalmed...why wait? Even 3knots an hour is better than zero.

I was thinking 7/8 for the design. Any pro/cons to each or both that any one would care to point out as a comparison.

Thanks
J

 

Hello Phil...

I have given this some thought.

This threat will never be an option on the design. I want to see a stick there regardless of what Father Neptune decides to do. When it comes to the stick, Force 8 as required by Category B will be exceeded.

I believe that I may have figured out the whole geometry thingie for a folding system for the mast, not much unlike others out there. Scary? Hmmpphhh...don't bend any sheets!

Update. It came to me while the beams for the sliding mechanism were chasing me in my nightmare trying to push me off a cliff by sliding open against me and they couldn't because they were binding. I think I have figured out a way to eliminate the "binding" nightmare I have been experiencing. I do mean eliminate entirely! Stay tuned so I can work it out in my head.

Thanks
J

 

Hello again Masalai,

Ooooohhhh... it looks like we are about to engage in some serious sail and rig thinking and verbalization. I also would like to peruse and comment, but will more than likely have more questions than opinions as this is not exactly my forte. Can we maybe drop a couple of other forms in there for discussion as it relates to the design?

Thanks
J

 

Hi J and Phil and Masalai

J, big jib means small main. Roller furl the jib and you have a good reefing option. Smaller main means shorter mast...a bonus for cruisers.

The main purpose of the 3/4 rig is to give the top of the mainsail good airflow. When the jib and main both end at the same point, the tops of the 2 sails become very inefficient because of the proportions of sail area and gap and mast, and the way this affects air flow.
The 3/4 rig is better for windward performance.

If you decide to get rid of the cuddy, I hope you don't change the internal layout of the cabins too much.

 

Hello to all...

I came. I saw. There was nothing to conquer...so I took all the covers off the boat and gave everything a good once over. This weekend will be for spring "boat" cleaning...which will help me to clear my head so I can continue to design the "first offshore rated trailerable catamaran".

I am contemplating the following name designations for the design.
TR27B...TR = for trailerable, 27 = for Loa, B = Offshore Category.
Comments? Suggestions?


Richard...
I am looking to streamline the layout and improve it if I can, but do not worry sir, it will remain as is. It would be criminal for me to have thought so hard to get so much use out of so little space to then change it when the Loa and Bm will remain the same.

I thought that sail efficiency has to do with shape and avoiding vortex at the tips? Would the 7/8 rig be that much inferior to the 3/4 rig? The design will carry roller furling and I'm thinking of furling the main horizontally into the boom. The main will probably be optimized with flat top and full battens since her area will not be extreme.


Now... on to Phil.
I don't have any idea what kind of space you have available at the bows of your cat, but I could not for the life of me get the bench seat to work. I gotta tell you...I really really wanted it really really bad, but, it became apparant that it is not for the design. Here are the findings.

Current Salon Condition:
Foot room is 1.5’L x 1.5’W
Seats are 1.5’ x 2’ at the crash bulkhead and 1.25’ x 2.52’ at the galley
Total linear seating is 4.52’
Total seating area is 6.15’
Backrest only on forward seat
Traverse backrest at aft seat against either bulkhead
Fixed seating for dedicated storage and refrigerated/ice box
Seat height cannot be reduced below maximum waterline for water tight integrity
Both sides of waterline protected even if holed between seats

Bench Suggested by Phil:
At the crash bulkhead, the foot room is .54’ and the bench seat is .89’ wide.
By the galley, the foot room is .81’ and the bench seat is 1.26’ wide.
Foot room is tight in all cases and may require lifting feet onto bulkhead.
The bench aft of the crash bulkhead is unusable for 1.5’ when it then becomes 1’ wide effectively reducing linear seating to 2.75’
The seating area is 3.16’

Negative results:
Reduced accommodations and comfort under all conditions for the same space
Unused wasted space
Reduced storage and refrigerating volume if at all possible to incorporate
Not enough space to slide into position
Waterline protection compromised in the longitudinal, traversal and vertical on at least one side.

Positive results:None can be identified for this design restriction.

Decision: Do not incorporate suggestion for design

I really regret not being able to incorporate this suggestion.

Okay...any one have any other suggestions I should consider to improve the design? Currently, I have one other from Phil (No Cuddy) to try to work out and decide.

Thanks
J

 

J, I wonder if I replace all my passengers with food supplies....my boat might be cat B rated....hmmmm

 

Hello Richard,

Hmmm...pulling the yoke on me huh? Whom will be there to eat the food?

Update,

I have been exploring the dodger/no cuddy suggestion by Phil. I like it very much and although it is rough I will make a decision when the cuddy is in place to see which one best fits the design. I may decide that a "fair weather" deck between the pits may still be an option but it would not be enclosed like a cuddy.

Picture 13 displays the TR27B on her light waterline. Although she looks sleek and streamlined and has pleasant lines, the dodger gives her more windage...4% more to 22% Loa. That is lots of windage but at least it isn't flat plates.

I imagine that it should be made in foam/carbon in order to reduce weight and increase strength. I believe an epoxy additive of 20% graphite and microballons by weight would reduce her surface drag for the same area. Headroom will still require vertical clearance.

Picture 14 displays the top view. I changed the colors for best contrast. I imagine that sailing will be on the windward side for many reasons, and the dodger provides excellent windward protection even without the telescoping tubes deployed for full headroom and enclosed protection. The inverted U tubes will be aft and forward and will telescope vertically.

Canvas and tubes will have to be rated for F8 or better so it appears that the cloth will be heavy weave and the tubes no less than 2.5" diameter. Seating will be quite comfortable and with a hinged board, each pit could provide a huge double berth for stargazing on clear nights. It appears that two helm stations may be required for this set-up. Also, the center panel above the companionways will have to be hinged so that head clearance is available to exit the cabins. The companionway hatch itself will also be hinged. The forward center panel and companionway hatch will both open forward and the aft will open aft.

Picture 15 displays her in perpspective and at work. I wanted to give some clarity to the above regarding the companionway, so I included the opening. The inverted U tubes will be attached traversely and inboard to the companionway bulkheads for support and they will telescope vertically so that headroom is achieved and any combination of enclosure canvas can be attached.

Questions or suggestions? I hope I was able to explain it well. I didn't make the outboard bulkheads for the dodger flush with the sides because it made the design look slab sided and I wanted some room for cleats. How does her nautical aesthetics fare?

I really like the way it looks. I won't decide until it is all roughed out for the cuddy also, but I think that these babies are here to stay and the cuddy will be excluded unless there are overwhelming reasons noted. Back to fun.

Thanks
J

 

J
I have always thought of a cuddy as something of personal preference, and have never been fond of them. They spoil the view of the ocean, add windage, raise the centre of gravity, add weight, and generally create a 'houseboat' feeling, which as you know, is not my cup of tea. You will never discover an overwhelming reason to have a cuddy, if you are designing the boat primarily for 2 people.
I am far more interested in your 2 super-cosy cabins.

No problem with the aesthetics. Looking good so far.

Can you point out the features on my design that stop it from being a category B?

 

Hello Richard,

The other Richard would be best qualified to answer this. He threw me for a spin when he glanced at my design and was able to state that it could be rated Category B just on a quick once over with very limited data.

This would be a bit difficult without having studied all aspects of the design, which I have not really done. My first observations are based on the stability results that were produced from the hydrostaics and specifics I got from your design.

I don't believe are high enough.
Stability # 0.903539
Stability Speed To Lift Hull 16.68627
Stability Capsize 1.8985

Get your hands on ISO or any other rating authority. It will help you to identify minimums for everything. On the other hand, you can just tell the NA to design it as such...but I suspect the design will change dramatically.

Here is the link for GermanLloyd to start you off. I have been on top of this for as long as I can remember and it still blows my mind. Proceed with caution for there is a possibility of losing your mind.

http://www.germanlloyd.org/infoServices/rules/pdfs/english/schiffst/teil-3/kap-2/englisch/inhalt.pdf


Thanks
J

 

Pits still there

Hello all,

I don't think the bench seat can work if you have the cockpits in each hull. If you get rid of them you will get heaps of room. On my little 6 metre cat - really small thing my sons each have their own berth at each end of the port hull and there is a 1.8 metre galley bench between them.

On our side we have a double with an area to stand up to put your undies on with your head poking out the hatch. Up front is the toilet with screen and in front of that is the anchor locker and under that stowage.

Heaps of well spread room if you don't have cockpits in the way. You will have the biggest cockpit anyway if you go folding solid floors and use the space between the hulls as the cockpit.

Another problem with th twin cockpit arrangement is steering. If you have a forward cockpit covered with a fabric dodger and behind it a sailing cockpit you can use a simple link bar with an extension tiller - good for a small cat. Your twin cockpits up front seem to be tricky in terms of steering, sheeting the sails and getting water down below.

I know Richard doesn't agree but in my over 5 years of living aboard multis I have always needed shelter. Waterproof clothing is not as much fun as sitting dry or at least somewhat sheltered. My 31 ft tri was a racer but benefited hugely from a solid windscreen and flip aft cover. My 38 footer has an open bridgedeck cabin so you can steer in a hybrid indoor/outdoor space. If it is raining you want to be out of the rain, if windy out of the wind and if sunny you want to be out of the sun - UV is a killer for anyone long term on the water.

If you use flip up seats on the inside of the hulls, go to a bench seat you will get heaps more interior room.

cheers

Phil

 

Hi J. Thanks for the link. If I was a law student, I might consider reading 1% of it. But I'm not.

I like this part though:

1.4 GL reserve the right to also classify craft
made of materials, for which no special GL Rules
exist, provided that proof of suitability of these materials
has been furnished.

If the rule-makers are flexible, I think that my trampolines with super-strong reinforcement netting, would pass the test easily.

This sounds like my boat:

II Voyages along the coastline, but restricted to a
sea area located at a distance not exceeding 200
nautical miles, measured from the main
land and/or from off-shore islands situated at a
distance not exceeding 400 nautical miles from
the main land 4 and/or from another island.

Sounds like category B.

I don't think my design layout would need to be radically altered in order to achieve the strength or stability requirements. In fact, I think my design will be stronger than most comparable designs.

Couldn't find any info on rules for onboard comforts. Seems like this.....if it exists on your boat....then it must be built to a certain standard. No flushing toilet? No problem.

So.....provided my sails are easily and reliably reefed, and I stow all the necessary emergency gear....my boat could easily achieve a category B rating.

So why am I saying all this?
I can almost GUARANTEE that your design will not be the first category B rated trailerable catamaran. Not trying to burst your bubble. Just don't be too disappointed if it's already been done.

Take care
Richard