Playing around with a 10 m trailer cruiser

Digital !! - Oh you techno nerd!!

I've been wondering how you were getting on.....
Couple of thoughts:
1. If you can move the windscreen fwd a touch, you might be able to squeeze standing headroom in the "lobby" of your fwd cabin area, by leaving it open above.
2. Have you checked against your waterlines to make sure that the sole extends as far outboard as you've shown it? It looks too wide to me at a glance- particularly up towards the berth. Also, I doubt you'll need 3 steps from saloon down to cabin - probably only 1.

The Open version is the prettier of the two OMHO. You could probably achieve a more closed in 'saloon' by doing something along the lines of the MJM 34Z ( http://zurnyachts.com/ )
with roll-down clears.

Though they're often frowned upon by many 'real' designers, I see no problem with using Gerr's rules for scantlings. Granted, they are somewhat on the conservative side, but they are well proven, based on sound engineering, and (provided they are applied correctly) should give a long-lasting and solid boat. I know of quite a number of well known, practising designers who use them for almost all their work.

What timber are you going to use for the model?

 

Something like this ?

http://www.boatdesign.net/gallery/showphoto.php/photo/1674/size/big/cat/500/ppuser/2043
http://www.tantonyachts.com/977ga.jpg

Seems to have a hinged top above what looks like a shower.

 

Tanton's "Search" does have some similarities to what I'm thinking of, albeit in a somewhat different style. It looks to be meant for longer self-sufficient periods than mine is, but he's got some neat features sketched in there.
The Zurn 29 and 34 mentioned by Will are a neat design that I might look at in more detail. I think I prefer real glass over plastic film for the house sides, especially in the cooler parts of the Canadian boating season.
Now, the sketches I posted yesterday were done in the back of a van a good 300 km from my computer, so no I have not mapped the actual hull shape onto them- these are just to toss around layout concepts, with the details to be refined later. I'm not sure how far forward I can extend the windshield without making it look like a houseboat-barge, but there might be a way to improve headroom up front while keeping the look I want.... we'll see after a few more sketches.
I've heard from a few people now that Gerr's rules are quite conservative; this is exactly what I want. The boat would be expected to survive for quite a few decades, weather the occasional bout of terrible weather, and live on a trailer- light scantlings just don't jibe with the requirements of this design. I've spent enough time working on ultra-lightweight carbon structures for solarcars in the last few years; for this boat I'd prefer solid and reliable.

 

Well, no, that's not really what I was suggesting. Just that if the space at the base of the companionway step(s) is open to the saloon and windscreen above, then you'd have full headroom there.
Search is an interesting boat - not too sure about the complete lack of bench space in the 'galley', or the height of the wardrobe that's imediately in front of the helmsman though....

 

The dreaming continues

In case anyone wondered where this one went, no it has not died. It's just constantly getting bumped by higher-priority projects. Getting rid of me ain't so easy.....
Another teaser here, of what might be coming soon. Been playing around with profile shapes; here's a slightly more protected version of the "open" profile from August. Yes it is just a wireframe superstructure, and yes the 3D is coming. It's faster to play around with wireframe for now though, since I don't have Rhino4 yet with its nifty linking of surfaces and the curves they came from. I figured I'd spare you guys the eye strain of another one of my digicam-scanned sketches.
I think I've settled on roughly the hardtop coverage shown in this one. Any more hardtop and you start to lose the open feel, but I want to keep decent and comfortable protection from rain and spray when the weather's less than pleasant.
There would be no physical barrier between the cockpit and the area covered by the hardtop; canvas sides and tonneau could be installed over the cockpit in bad weather.

 

How's the model coming along Mat?

 

Slowly. It's fully framed up but I have yet to buy and slice up the 1/8" veneer from which the planking strips will come. That'll get 1 mm of fibreglass overtop before being faired smooth. A loose approximation of the construction method of the real thing. It shouldn't take that long but other, higher priority projects keep displacing it..... I'm sure everyone's familiar with that feeling.

 

I've considered waterjets for all the same reasons, right up until the price kicks in. I dont know why the costs are so high (around 6-10k) for that kind of propulsion.
My project is smaller, under 30ft to fit in a container - so I wondered if a waterski setup could be incorporated.
I had a 26ft macgregor that did 18 knots on a 50 hp, so this project seems very feasible. But I would like to keep the sailing ability also, but with an interior steering station for non sailing weather.
The lines on this project are very interesting to me.

 

It doesn't make much sense to me either, why they're so expensive. There are cheaper ones, too- an Aggressor "Junior" series is worth around three grand- but that's a high-RPM, lightweight-boat pump for 50 mph plus. Those options will be considered as well on this project, in due time. And I haven't ruled out a Duoprop or Bravo-3.

Sailing ability will not be a factor on this boat- I'm trying to optimize for an efficient shape at low planing speeds under minimal power (in the end, the power will likely trace back to either biodiesel or cellulosic ethanol, both of which will be widely supported by the time she's launched). I do wish there were more boats with the combined power/sail ability of the Macgregor; they seem to have some interesting performance traits that should be further developed by a bit of healthy competition.

This link http://www.woodenboat-digital.com/woodenboat/20070910/ was posted on another thread recently, it's an excellent description of an adaptation of a jet-ski drivetrain to a "real" boat. I have not ruled out using one or two of these units here, but I have yet to do the research on the feasible propulsive coefficients and thrust curves with such a setup.

As for the model testing- finally getting back on track with its construction; today I started laminating the sheets of birch veneer to plank the tow test model with. Time for this is of course a bit scarce but I'm figuring on having the model, towing rig, measurement systems, etc. suspended off the gunwales of Sunset Chaser for the start of boating season '08.

By the way, the scantlings (as of this time) will be more or less based on the method outlined in Gerr's Elements for wood-epoxy strip plank (leaning more towards the epoxy-sheathed strip-plank-on-frame types than the strip-plank-cored-composite types in this case), with a scantling number of 1.26. Those calculations, plus proper engineering analysis where I deem it fit, are in progress.

 

Another teaser

Just in case anyone thought this concept was gone.... it is not. At last, there is a 1/6 scale fibreglass model sitting in the basement. Still needs a deck and a bit (ok, a lot) of fairing mud, but should be ready for next boating season....

Parallel development is progressing, now, on a second, smaller vessel based on the same parent hull. This would be more of a day boat, or a weekender for two, than the 10 m version (which, as you may recall, is intended to be a weekender for 4 or a cruiser for two). Targets for this version are a length of around eight, maybe eight point five metres overall, displacing no more than 1500 kg at the dock (2100 kg with crew and cargo). (I'm working on bringing the vessel weight down below 1200 kg when on the trailer, which would put towing comfortably within reach of vehicles such as minivans, that do not have thirsty 300 hp diesel engines.) Power of between 100 to 150 hp would be fitted to achieve calm-water speeds approaching those of the big boat (which is intended for 25 knots at WOT with typical loads). Although the smaller version will sacrifice some rough-water capability, its bottom loading would be around 20% less than that of the 10 m craft, which should translate to a slight improvement in planing ability in the 10-20 knot range where it would spend most of its time.

I'll be back with more soon.... (and by soon, as I'm sure some of you have noticed, I likely mean within a few weeks )

 

Boat's looking great... but I note you still haven't tidy'd the workshop...;-)

 

Mat, what kept you from going the double wedge route instead of the warped plane with a v aft? I like the concept of the boat very much, but am curious what kept you away from the lobster boat shape and the extra efficiency of a dead flat at the transom.

Looks good!

E

 

E,

I'm glad you like the concept I am hoping that something will eventually come out of it....

Why doesn't she have a lobster boat style shape at the stern? Well, to be honest, I did consider flatter-bottomed hull forms, and forms with an upward-sloping run, in the earlier stages of the concept (before this thread). From what I've seen and read (and I haven't spent any time on lobster boats), these vessels are extremely efficient for what they do. Their hulls are optimized for inshore running in ocean waters, at semi-displacement and low planing speeds with significant loads (I have heard of a 4-tonne, 9-metre boat of this style that broke 20 knots with a 200 hp diesel).

The inland lakes and canals this boat would be intended for (plus the coastlines of the Great Lakes) tend not to have the relatively big, rolling wave systems found over the Grand Banks. We tend to have short, confused chop coming from all angles, at a shorter wavelength and smaller amplitude than would be expected for a given wind condition. So the ability to maintain a steady slow plane in this kind of sea is substantially more important in this design than is the ability to keep a comfortable motion in big waves, as is paramount in an inshore working boat. Both the 10 and 8 metre versions of this craft are intended to be very light boats (for both efficiency and trailering/launching reasons), with very low D/L ratio and relatively low bottom loading. They're too light, it seemed, for the lobster boat forms to be able to maintain their proportions at this scale while retaining their advantages over the shallow-V. (I should note that while the maximum 3500 kg displacement at full load remains for the 10-metre, I am trying to lighten things up considerably in the unloaded condition.) Add to that, the minimal-draught requirement, the desire for both jet and prop possibilities, and the desire to maintain relatively even trim with little discernable 'hump'- hence the high-lift, low-bottom-loading shallow-V form which is currently being studied (but which, I should note, is not necessarily the final form of the boat!) Given the slightly higher speeds at which this boat would run, and its somewhat lighter weight, I am keeping a bit of deadrise in there (although with each successive iteration, the deadrise does seem to decrease a bit).

So in short, as much as I love lobster boats (and am taking styling and functional cues from them in many cases), the capabilities required here don't seem, from my perspective, to mesh with the design intent of a craft designed for what is, in the end, a rather different type of service than this one will see.

(A further note - the powering calculations done on the 10 m version so far indicate that with the jet drive at a propulsive coefficient of between 0.5 to 0.55, we would be seeing at 3500 kg displacement, a cruise of 19 knots drawing a hair over 130 hp, and a top speed of 24 knots at 175 hp- I think this compares reasonably well with the 4-tonne lobster boats I've compared the design against, typ. 16-17 kts @120-150 hp and 20-22 kts @ 200 hp. Or put another way, this one might need about 1.95 hp/tonne/kt at 19 knots cruise with the jet drive, roughly comparable to those lobster-style boats' 1.8 to 2.2 hp/tonne/kt at their typical cruise speeds. I suspect the added drag of the long keel/skeg seen in most such craft compensates for the relatively greater efficiency of the large, straight-shaft props.)

(ps- nice blog, E, btw! dangerously addictive reading.....)

 

Thanks for the kind words on the blog. I needed a creative outlet for my somewhat disjointed thought process, so why not entertain people at the same time, right?

So I can understand the additional beam aft, keeping her more in the warped plane territory than the double wedge. It seems to be not only more efficient, but might allow more accomodation per square foot of boat. My boat, during the sea trials for example, had alarmingly higher performance for her given design. The hull is warped to a 0 degree transom, and she gets along at about a 12 mph advantage over her intended speed (a 40% improvement with 20 additional horsepower). This has an unintended consequence of pounding at speed, which the V would seem to mitigate a bit id imagine.

The other question thats really rattling around on me right now is the rooting issues. These warped plane boats have a nagging tendency to root and broach in a following sea at speed. Long, lean boats with a lean forefoot, lots of lateral plane, and a little speed tend to come around unexpectedly, and most will add a skeg of significant size to protect against this. Mine is no different, as im sure you've seen in the blog. Is this going to be a consideration? It definitely throws a wrench in the works for the pump. Im wondering if you are thinking of something along the lines of strakes, bilge keels, or if the V allows enough stability to prevent or reduce the tendency.

Im definitely seeking an efficient design in the 8m range, one that can fish, and be a coaster for my wife and I in the Inside Passage. This has the right personality. Is this something along the cabin profile?:






Jacques Mertens, www.bateau.com ,penned this boat. It really has some pop, but I prefer a forward tilted workboat windshield, and at 6'3, enough headroom to stand.

Always enjoy watching designs unfold! Now, back to work (2 heart attacks, a stroke, 2 car wrecks, and 5 other various calls so far today).

E

 

I'm hoping to get some answers to these questions from the model tests this spring and summer, E. At 1/5 or 1/6 scale, it should be possible to duplicate such a tendency should it exist.

It seems a lot of jetboats, especially those of this general form, do have at least a slight tendency for the stern to kick out sideways in a following sea. If this is the case here, there are a few possibilities- twin small pumps and a centre skeg, single pump and bilge keels/strakes, jet intake nacelle, a counter-rotating sterndrive.... I'll wait until I have some test results to figure this out from.

My current boat (based on Phil Bolger design #432- "Diablo") has a two foot wide flat pad as the centre of the bottom, with a deadrise of about 26 degrees for a foot and a half either side of that. Amazing boat, fast as a bat outta hell, but you need a substantial load to prevent her from pounding in a short chop. Given that the new boat has roughly comparable bottom loading and displacement/length ratio, I think a slight bit of V is necessary to reduce the pounding effect. Transitioning to a flatter deadrise at the stern might be possible with a sterndrive or inboard variant, but goes against everything the jet suppliers say is best for their units.

The Mertens design mentioned above (the Down East 25, if I'm not mistaken, http://www.bateau.com/proddetail.php?prod=DE25Cockpit ) is a beauty indeed- she does share some similarities to this boat, both in possible layouts and general style (the hull is of similar type, although it appears optimized for higher speeds than mine). It is marginally faster and a bit smaller than both the 8- and 10-metre versions of my current project; still, a boat worth investigating further.