Sueños Mojados

OK, he's mounting an outboard on each stern so you'll need a flat stern. The design does look fuel efficient. You might contact them to see if he will sell plans so you can build per blueprint. If not, search around for another comparable set of plans. I did a quick search and found this plywood/fiberglass design. Plywood boats are typically easy to build and repair. They can last for years if you take care of them and stay on top of fiberglass repairs. A good UV coat of paint will help protect the fibers from the damaging sun rays.

http://www.glen-l.com/designs/outboard/aquacat.html

 

This is the transom pic of the Sliver 38:
(taken from http://www.supercat.co.za/supercat_38_sport_custom.htm)

Notice how the transom rises gently and is not a deep prismatic section as yours. hat is a well-done wet transom which will create some drag at low speed (but much less than yours) and will allow for good high displacement speeds.

I can't find an equally good pic of a Sliver 29, but this one hints that the design principle is the same:


- and it makes 21 kts with 2x40 HP outboards.

So, what it tells me is that something is visually wrong with your design and that imo you should review it, because a very similar existing boat has very different hull lines yet gives a better performance than what is set by your design goals.

Don't take these considerations negatively. They might save you from a costly failure.

Cheers

 

Agreed daiquiri. The transom on that Silver 29 looks pretty good. I think a set of plans for this or a similar kit boat would do the job.

 

Here's a link to a 30ft Tahiti CAT. Plans available. The construction looks less complex than the Silver 29 and you get a bit more shade from the sun.

http://kelsall.com/Designs/KSSP30Tahiti.htm

 

Damn that Custom 38 just looks slippery! Reminds me of spanish mackerel and sailfish

Its very difficult for me to draw like that in the program that I am used to using. But! I can assemble like that with HDPE.

You guys have given me pause for thought but the first thing that comes to mind is that one option that remains available is to draw and cut and weld along the lines that I have modeled and test that then add a pod shaped like that with manual shaping and aligning on. About another 5' section or smaller pod. Will have other benefits

I know some guys seem to think I am pig headed about my choice of material but I am going to be build one out of PVC foam or PP honeycomb sandwich. That will be the Woods designed one

Actually the closest existing plans to what I want are the Woods Skootas and Wizard. And the Wizard warrants a closer look with the flatish open all around walkability that I desire, especially the boat in the walk through vid. But its setup for sail and only a small outboard

 

The Skoota 20 is available with an open deck and no cuddy. The Wizard is a sailing boat so of course has a different hull shape, which is not efficient for a power boat going over about 6 knots.

Richard Woods

 

Richard, hence the Jazz 30

Joseph, Daiquiri
Borrowing from Jeff's suggestion, this is what I meant. The way the drawing program I am using, it doesnt allow a complex line as it provides only 4 bulkheads and then dragging lines to fair. But, I can draw a pod that way too and by entering numbers in, I can get an accurate match where the hull transom is. I just quickly drew this to show what I mean

pod by jonny.toobad, on Flickr

 

Just a thought but your intended use for this design could be constructed also with modified "skin on frame" method. Rigid "keelson" along the entire length of the hulls
(and where the bridgedeck is fastened) to give longitudinal stiffnes and support kayak like flexible frame with longitudinal stringers supporting the "skin" which could be considerably thinner and the produce a lighter boat.

Like I said just a thought but could be better solution against the beating you're intending.

BR Teddy

 

Saqa,
my vision was much less complex..... just continuation/extension of the hull sides & a swim end of about 450-600 mm length with the bottom transition as a step to it. That looks to me very long & skinny putting your outboard weight out a long way with little buoyancy contained & narrow so outboard steering etc goes where?

Jeff

 

That picture also hints at design/marketing principles of the Wharram craft....

 

Don't focus on the transom too much unless you really want a boat for 10kts... the sliver 29 is only 1 approach, there are plenty other successful designs which have a much fuller and deeper transoms. A simple 25ft cat, should be able to achieve much higher speeds with 2x40hp, so the question is- do you design for 10kts and use smaller outboards, or keep your twin 40s and design for closer to 20kts? I actually modeled the super cat style hulls in free ship a few years ago as I was curious about their characteristics, i also ran the models through michlet for resistance estimates. After drawing up various 3d models and looking at the hydrostatic trends and michlet results, it became clear that they did suffer from 1 handicap and that is wetted surface area. For their displacement, that shape has more wetted area than most other typical catamaran shape hulls.

 

Heres another design you may not have seen, a 33ft powercat powered by twin 40s and heaps of mod cons weighing it down, still manages speeds in the high teens;
Utilizes the Malcolm Tennant canoe stern hull form - which is pretty similar to the supercat style shape when you think about it, however the canoe stern is easy to build from flat or 'developable' panels as opposed to the supercat round bilge stern...

 

Looking at the rear end view of the Sliver 38, it is still a guessing game as to the actual shape of the hulls. However, the fitting of those bolt-on outboard fins suggests it might squat a little.

 

Well, there are endless examples strewn around this forum which i noted previously, you are electing to ignore them, fine that's your prerogative. But it is clear your understanding of this is very different from mine. Your opening gambit is thus:

“hey guys I have an idea, what about this….or….this…etc”.

And it becomes a pattern of you allowing others to “solve” or “show” whatever “it” may be for you. Again, nothing wrong with this, many do this. But you’re deluding yourself that YOU are solving and such issues and coming up with the solutions and logic yourself. And without any real objective other than the question as a standalone issue. That is not boat design.

Designing a boat is greater than the sum of its individual parts…which is why a proper decent SOR is required, not a collections of ideas that are often competing with each other (often laced as a question not a requirement) and provide no realistic solution save for a debate and chatting about it as an idea and concluding YOU designed it.

The assertion is thus:

So, lets look:

Hmmm….sounds familiar.

Hmmm….sounds familiar again, QED.

And then it falls down when the “formal” education as you put it flies in the faces of what you want:

It’s admirable you wish to build your own boat. Groper has been doing one for years. But you’re under the illusion that it is simple, yet you are constantly seeking advice (ergo it is not so simple), then the usual pattern ignore comments that do not go with your grain, and then getting all emotive and upset when such ideologies do not match your expectations. Your emotional (impatient) side is blinding you from issues that need to be addressed, but your impatience gets in the way of that logic and reasoning.

I work in the commercial sector, where the money invested is considerably more than the amount you are investing in your project. One client has steadfastly refused to listen to advice and going down a very similar path that you are heading. It has taken him several years to build his own boat and adding features that are not logical or sound or have any technical merit. Yet his inability to listen to reason and common sense because it does not align with his “ideas” or that he is 'designing' it himself by making such choices has cost him a large fortune.

Again, never said such a thing. Your emotions are subverting your comprehension and getting in the way of facts, again.

You note above your SOR.

Your SOR on that forum is here:

http://forums.bateau2.com/viewtopic.php?f=28&t=59740

Again, this is far from an SOR, it is just a collection of thoughts and ideas that you’re throwing out to everyone (just as you're doing here) under the assumption you’re not seeking advice. Richard very politely gathered all your ramblings in an attempt to get some idea of what on earth you want and if it is indeed possible.

His solution is here:

http://bateau.com/studyplans/Jazz30.pdf

You’re only focusing on those singing to your hymn sheet...fine, if that’s what you wish to do, good for you. But be under no illusion that you’re not doing this all yourself. Your endless threads clearly suggest otherwise. That is clearly where we differ.

 

Either that or the transom might not be getting dry at the desired speed. Hence, perhaps a tad too deep wet transom on that boat too.