Old 3 point hydro build...

[Suprathepeg]

So I picked up this old 13'-3" hull. Its been sitting in a field for 20 years. The bad news is its a mess transom is shot, no controls, no motor etc. It has a gas tank but its metal and its had fuel and maybe water sitting in it for 20 years. The good news is its a super simple design the two halves just clam shell together with pop rivets, the floor is the bottom of the hull so there are no stringers or floor to replace, the transom is literally just plywood glued to the hull. So here is my plan. 1. split the hull and remove the old transom wood etc. 2. glass in a new transom and some new seat bases. 3. install controls. 4. strip and repaint the upper hull (bottom is pretty nice) 5. some sort of stereo The only gauges I"m planning to run are tach and temp. Here are some of my questions so far: 1. How should I power it? In its past life it wore a 40hp. I think I can get my hands on a merc 50 or a merc 75. The 50 is probably a better match for this small hull but I wanna hit 50mph so how should I prop it? 2. Would this be a good boat to swap in a jet ski power train? The benefit I see with this is that it would be a great shallow water boat and it would probably be lighter than a full outboard. It would be a lot of glass work but probably not too bad. 3. Trailer suggestions? 4. I have a plastic outboard tank, should I try and salvage the existing steel one or make use of the plastic one?? 5. Seats? This thing used to have two back to backs, I think I wanna make it a 2 seater. I was thinking of using small buckets like go cart seats but I'm 230lbs so it would have to be big enough to fit me. Any suggestions?

 

[lckstckn2smknbrls]

I'll be following along.

 

[Suprathepeg]

No Title

Here are some more pics of how it has sat for the last 20 years

 

[Suprathepeg]

I need to figure out the seating for this little scooter. Its going to be one of the first things we have to do so we can setup the new interior. I want to keep things as light as possible, if things are going to be heavy I want them to either be fuel or the motor that drinks it.

This thing used to have back to back seats that were bolted to two 2x4 cleats that were glassed into the floor.

My criteria for seats are as follows:
1. Weight, I want to keep them as light as I can.
2. Support. I want them to have enough support that you don't slide around or out of the seat easily at speed.
3. Comfort. They need to be comfortable enough that I can sit in them for 2-3 hours and still be having fun.

Lets figure that the back to backs weighed 40lbs combined (probably more but whatever) that means the new seats need to be less than 20lbs a piece.

I was looking at these:

Mod EDIT

I'm liking these under 15lbs:

Mod EDIT

Anyone use the above and have a comment? Maybe an alternative?

Mod EDIT: Please remember iboats sells seats and avoid posting links to other retailer's products

 

[Suprathepeg]

No Title

Got the wee beast to the shop today. It's pretty light, about 300lbs. I think I'm decided on going with outboard power. It's gonna be easier than a jet. Using the coast guard formula this hull can handle 45hp. However being a 3 point and thus having more than one footprint in the water it shouldn't be limited by the formula. So I'm looking at 50-70hp outboards. Weight is the concern.

 

[jbcurt00]

I'd be interested in how a transom as short as this and the multiple point hull effect the hp calculations.

From the info I'm familiar w/ for an outboard boat w/ less then a 20" transom (yours is quite a bit shorter) :

Max hp = (0.8 X L X W) - 25

Where L = boat length along the centerline (you posted boat length13.25ft), W = transom width, and you came up w/ 45hp max?

45hp = (0.8 X 13.25 X W) - 25

65 = 10.6 X W

W = 6.13

Yields a transom width of a little over 6ft, it doesn't look like it's 6ft wide at the transom.

If you used a multihull calculator to estimate hp, I'd be interested to know where you found it. I couldn't find one.

Good luck w/ the project. Boat looks like it'd be a real kick in the pants w/ a 35-50hp OB.

Try to remember the host of the forum is a retailer.

 

[Suprathepeg]

There is no calculator for a multi hull.

I get that Iboats sells boat seats. I'm looking for input on using car racing seats which obviously Iboats doesn.t sell.

 

[jbcurt00]

But the sites you posted links for do sell boat seats.

Just copy the pix and post the pix w/out the link or the site info.

So the boat is about 6ft wide at the transom and you used the same USCG formula I did?

 

[Suprathepeg]

No I used the standard height transom formula, either way I don't think the formulas matter as this isn't a mono hull. I'm just using them as a reference point, a starting point so to speak.

 

[fhhuber]

With the narrow transom vs overall beam and an outboard hanging off the tail, that thing will squat and if it squats far enough (too much motor) its going to sink.

You may want to do some figures on keeping the top of the transom above water when the boat is slid off the trailer.

 

[scoutabout]

Cool project. Transom is quite short - you may want to consider a jack plate? Also any seat you are going to spend a couple of hours in should have a seat cushion long enough to support your legs a bit which in this boat is going to mean you get them up off the floor. I like the idea of going to two buckets.

Good luck with this. Looking forward to following along.

 

[Suprathepeg]

With the narrow transom vs overall beam and an outboard hanging off the tail, that thing will squat and if it squats far enough (too much motor) its going to sink.

You may want to do some figures on keeping the top of the transom above water when the boat is slid off the trailer.

Yea launching angle is a good point. I think we're gonna have to build bunks on an old trailer anyhow so adjusting the angle the boat sits on the trailer shouldn't be a huge deal.

 

[Suprathepeg]

Yesterday I had some time to look at the boat a bit more. So the floor of the boat is made up of the hull, 1" rigid foam with a layer of glass on top. I guess the foam was the flotation. I think I'm going to change it a bit to add a bit of a bilge so I can install a pump, The free board is so low that I can see a lot of water getting inside while running about.

 

[Corjen1]

Cool project, mind if I tag along?

 

[Suprathepeg]

Tomorrow morning I'm going to look at a donor boat with a 50 merc and a trailer etc. Looks like it will have everything we need except seats (which I'm still debating) including maybe a short shaft lower for the 50 which would be awesome! Cros your fingers for me that I can swing a good deal!

 

[Suprathepeg]

No Title

So this boat has 3 flat planing surfaces the two front ones are approximately 4" below the bottom of the rest of the boat. I'm curious should the cavitatiion plate be set to the height of the transom or the front planing surfaces?

 

[Suprathepeg]

No Title

Donor boat secured! Someone's incomplete project becomes my new donor. Boat was $500. Came with a really nice trailer, all the controls and a merc 500 with good compression and lots of spark. The hull has been refinished and it has a new floor. It's too bad cause it'll basically be garbage when I'm done :-D.

 

[K-2]

You are missing something there.
I don't see how a motor mounts to that low transom.
Is that old caulking on the outside of the transom?
I'm guessing there was some kind of mount, jack plate, whatever, mounted there.

 

[Suprathepeg]

Yea I'm gonna build a jackplate out of aluminum angle. I gotta do the transom on it so I'm thinking that I may fill those holes and make the jackplate narrower than what was on there before.

 

[Suprathepeg]

Having glanced at your resto post these are my thoughts. Skip the temp gauge and get a water pressure gauge hooked up,with no thermo in these motors you should be more concerned about getting water to the block.Seats,just get some fiberglass style cafeteria ones,lightweight and easy to pull the legs off and make a base for them. Your not going to be out there for a long time as the hull is going to demand flat water and most lakes by noon have enough boats roaming around that you will have to pull it out. So big buckets are just dead weight and you are not going to be cruising around in this for the day..You say your going with a jack plate,so if you cant find a short shaft motor build your plate 5" higher and use the long shaft... 350-450 dry is not that light for a hydro so the 50 is in no way overpowering it IMHO.

Water pressure is a good idea, I'm going to look into that. I want to run some sort of engine monitoring guage (temp/water pressure) and a tach, maybe a volt meter too but we'll see. I've already started the jackplate and I'm making it for a long shaft if I can get a short shaft setup complete then I'll just cut it down, no big deal. I've been hunting for the type of seats you mentioned but everything I find locally is more expensive than the racing seats that I've seen online and probably weigh the same.

Power wise, If the 50 feels weak and it seems like the boat can handle the weight I'll probably just put a 70 on there, its only an extra 10 lbs. The big question that I haven't been able to answer yet is with so little free board can it take the weight. I plan to reinforce the hull anyhow with maybe a stringer depending on how I mount the seats.