own design or plans?

[copenhagen]

ok i know this moght sound like a silly question, but i was just about to start building a bateau phantom 16 (my first build was a 14 foot S&G jon boat from said company) when i found a 150 horse 2 stroke tohatsu outboard...

i have a half finnished rennegade 16 foot hull (which is 12 deg deadrise) but the primary use of the boat is as a skiboat in a lake so it wont see waves bigger than 6-8 inches and usually no more than 5..

so i first boughtand studdied the ph 16 (and gv 15) plans intending to add the 150 horse tohatsu but now im having grandiose plans of designing a hull myself...

the boat we ues now si a 14 foot vator with a 70 hp evinrude and we need more oomph... so i thought id design one myself it will need to be aprox 2x5 metres, have low to no deadrise (its a skiboat) and be as light as possiblë

ive dabbled alittle with the lines and have come up with the below... it would be built as a foam sanwich... up side down on a temporary jig consisting of osb frames sovered in 15mm soteco F80 foam, glassed with biax 400 and rowing, tured over in a female temporary jig, be glassed wit stringers and a 150 mm selfbailing sole...

im aiming at 150-200 kg bare hull... the floor will be 20 mm foam sanwiched between door ply and covered in 200 g rowing and epoxy...

but my question is "is this totally nuts or relatively sane... ?" perhaps i should do it as a s&g in 4mm ply and cover it with core foam inside and glass outside and in? like a "lost mould one off build"

[PAR]

Totally nuts.

It takes a considerable amount of study to develop the lines and engineering responsibilities for a high speed planning craft. I see a host of issues with your proposed FreeShip drawing, most typical of a novice designer. This isn't a personal dig at you, but an observation, based on your comments and drawing. This doesn't even address the structure engineering and it's expected loading, from a variety of sources, particularly if you're interested in a light weight, stiff and strong vessel. The design of this type of boat requires a special emphasis on expected strains.

[copenhagen]

I propably should have mentioned that im a mechanical engineer and have built 2 boats... so that task is albeit big, not impossible to undertake. the rigidiy of my design comes mostly from the box structure with high modulus fible on all sides.. (6 parallel boxes comprised of the hull bottom, the 5 longitudinal stringers and the floor) but i agree that it isnt a light task..

but please elaborate with regards to teh "host of issues".. the forward 90 cm of the bottom isnt developable but that was an issue with freeship (or me as om used to autocad) and the transom isnt even in the drawing... .. i plan on doing it in single curvature panels.. no double curved panels... the general layout though, 3 degree deadrise etc.. is it viable??

the interior layout would be somthing akin to a linder 460 with the box structure of the forward bench seats taking the twisting loads where the sole is thinning towards the front of the boat..

seriously though.. i would really like some input here.. personal digs are ok, but please include tips or links to literature too ;-). is the general idea of the hull form ok?

[Dean Smith]

I want to encourage you. After all we must begin somewhere.Most boats begin of a idea in our heads, it keeps us dreaming.
But IMO you need to get the concave out of those sections forwards
once you get the lines right you can run the structure past the forums.
Weight will not be an issue and you could use 4 box ply girdars to really stiffen the boat
Do not forget vee gives strength in form of shape and will help the boat turn.

[copenhagen]

im trying to get rid of the undevelopable curves now.. but it seems ill have to import the chinepoints from a .txt file so itll take some calculating...

and the flat bottom in the back is purposely flat to keep the wake smooth... and btw,, since it is this flat and light i think it lends it self rather well to a hull step... bit im not sure how much it will really add.. although it seems to me a very large wetted area for a 500 kg boat as is....

pointers please :-)

[tom28571]

If I see the aft section lines correctly, the chines rise quite a bit while the keel stays straight. If so, I'd not like to be in this boat with a big motor on it. No telling what it might do but it would not be pretty.

[Dean Smith]

Originally Posted by tom28571

If I see the aft section lines correctly, the chines rise quite a bit while the keel stays straight. If so, I'd not like to be in this boat with a big motor on it. No telling what it might do but it would not be pretty.

Yes make it monohydron. But carry on!!! cant really see much can you post iges or rhino file

[PAR]

I don't have a problem with warped bottoms Tom, but that set of shapes will be problematic to say the least.

The list of "issues" I mentioned Copenhagen, are extensive and most students of design will catch many of them. To list them all would be a bit beyond the scope of a discussion forum (a dissertation of yacht design), but some things to think about are the aft waterlines, which are dead straight and will make a difficult to steer boat, probably a "walker", and appropriate deadrise for your intended waters and use. Clearly a weight study hasn't been preformed, other wise the boat trim would be more representative of reality, rather then the drawing here, which shows the keel parallel to the LWL (150 HP outboards are 180 kilos, plus fuel and controls) Lastly the suitability of the hull form for it's "targets". Given the estimated 200 kilo bare hull weight and 150 HP, this boat is going to knock your dental work out, so suitability for the roles it's expected to preform should be a prime consideration.

[nukisen]

The only hint I can give to you Copenhagen as i assume you want to use this one in Öresund there is not very often the sea is clearblanc. I think you will have a bumpy ride with this one. I suggest you take a look at others deadrise to get through this. Try increase deadrise and you will get a softer ride. Else I like the enthusiasm and also the first design. The reason I give you this suggestion is because I live on the other side of Öresund. As we live here we have to compromise a little bit with weather and the resistanse. At the same time we dont often have very rough weather. So I suggest you compromise someway in the half way. At the same time you do have a lot of power to compromise from. This sounds really fun for me. Maybe we meat at the water some day. Though my boat does have 143hp less. hehe
Just take it easy and figure out what you are dealing with and very soon I think we have one more designer in this forum. Even if me myself only counts as a hobby designer.
We do have some really good proffessionals in this forum gladly posts help to us who have a long way of learning in future. Most of the proffessionals inside here is worth all the respect we can give. Do you agree Par? hihi
Ithink Par is one of them who have saved a lot of money and health for others inside this forum with his hints and suggestions.
Par is one of them who is really worth the respect given.

[copenhagen]

nukisen.. actually the boat will be run on "Immeln" a lake in skåne so its right in your back yard.. which is also where the 14 foot jon boat (garvey 14) is being used.

have been styduing the lines of both the ph16 and gv15 which i have plans for and will do a 2. revision of the hull lined based on the ph 16´s hull bottom ill try and extend the hull by about 5-10 % and raise the freeboard according to my draft above.. that way i wont end up with an illhandling boat... albeit it will be alittle overpowered when not pulling a skier

the size of the boat is dictated by the boathouse we park it in and its 2.55 x 6.30 meters inside the "dock area" (the outboard weighs 149 kg by the way)

[tom28571]

I think I misread the shape of the aft section drawing which may have been confusing. I don't have any problem with warp in aft bottom sections in general. It depends on the speed potential. If this boat is to be very fast, aft warp can make for ill handling at high speed. Most high speed boats have the monohedron aft bottom shape which I find to be more dynamically stable. The warped aft bottom is quicker to get on plane with more lift aft but introduces handling problems at higher speed.

[PAR]

I agree completely Tom. I have a large warped bottom Chris Craft that maxes out around 37 knots. It has a lot of drag above this speed, so it couldn't be driven much faster, but on small, over powered warped bottoms, I've experienced high speed stability issues. The above drawing will be one ill handling thing, that's for sure, especially if well powered up.

[copenhagen]

hmmm the bateau phantom 16 has the very same warped bottom albeit alittle more deadrise... so what to do then... keep the monohydron glen l 16 foot outrage hull i have in semifinished form and forget that its 12 degree deadrise.... ?

[nukisen]

Aha this explains a lot. Actually our kids are going for scoutcamp beside Immeln this summer as there will be a very big Jamboreen there this summer with over 50 nationalities from all over the world. I have been paddling around on this lake for some weekends also.
I suggest you listen to what Par and Tom tells you about the high speed issue. They really know what they are talking about. In this high speed there is big differents with small changes of the lines. With 150hp there is a lot of power to compromise with and still have an incredible fast boat.
I can bet you will not regret if you show up the boat you designed and the result of what people see is an emasing fast boat and people are talking about how stable it is in high speed.
Both Tom and Par knows what they are talking about as they have done this for ages.

[nukisen]

Sorry! I did post after you have allready answered "Copenhagen".
The little more deadrise means a lot i think. And wont destroy the shape you have designed either.