add a pad

I have a 1648 flat bottom that I installed a 140 mercruiser and stern drive in. I have been disappointed with a top speed of 35mph. I plan on rebuilding the hull and installing a long pad. Starting narrow, about 8' from the rear and spreading out to 10-12" wide at the back with a strake on each side like the hull pictured below. Any thoughts?

Any pictures of it underway? My first thought is that engine looks way to heavy for that boat.

Call me a SISSY - but, IMO, 40+mph in a flat bottom Jon is WAY TOO FAST !!!
As the saying goes: There are fishing boats. And there are racing boats.
There never should be racing fishing boats. [-X in the Jon Boat (flat bottom) design.

I will post pics once I get started.
I believe bass boats run 60 plus and catch fish. I have a history of building things no one has seen before. Some work and some don't. Its my hobby. If a hull of fiberglass and foam doesnt work I will simply remove it. I would really be happy with 50 mph. :shock:

lkirkpatrick said:

I will post pics once I get started.
I believe bass boats run 60 plus and catch fish. I have a history of building things no one has seen before. Some work and some don't. Its my hobby. If a hull of fiberglass and foam doesnt work I will simply remove it. I would really be happy with 50 mph. :shock:

Click to expand...

Bass boats that run that fast don't have flat bottom hullshapes. But good luck to you! I'm not gonna tell you what or what not to do, but I don't have much advice to offer. Keep us posted with the progress and results.

Only thoughts I have are:

Full face crash helmet

Extra good life vest

not necessarily in that order, but both are advised. While water is easy to move or displace, when a human body hits the water at speed, water turns to concrete for some reason or another. Don't ask how i know this.

Good luck with your venture.

Will not work. Have to be above 55 to make a pad work.

Its the weight that's killing you, gotta be.You could try a whale tail or custom make a foil for the outdrive.Get that heavy *** out of the water.Always fantasized about putting a modern 4-cyl car engine in a small aluminum boat but don't have the skills or resources.Its amazing how much power they are getting out of a 2litre motor these days.Know a guy who customizes old Hondas from the 70's and puts late model motors in them he wins car shows against $100k lexuses .A 4cyl Honda v-tec puts out 170hp and is all aluminum probably half the weight of the Iron duke.Good luck with your project and don't listen to the nay-sayers.Safety wise use your common sense you should be fine.There are a lots guys ripping around in ridiculously over-powered lake boats in log-filled rivers with very few accidents.Drunken idiots should stick to certain lakes where they can only kill each other.Cheers m.w.

Thanks muddywaders. I am committed to this project and I am going to modify the underside to try and lift it some. This boat as a whole is WAY lighter than the ski boat I removed it from. If I ever get to run 45-50 mph that doesn't mean I will drive wide open all the time! 8-[

Any chance you are under or over propped? What kind of RPM are you running? The right prop can make all the difference. That being said, you are really tail heavy. I'm no expert, but prop designs can dictate many things aside from forward thrust. Cupping, raking, pitch, 3 blade vs 4 blade vs 5 blade, SS vs Aluminum, all will have an effect on overall performance.

If that motor/outdrive combo came from a bigger glass ski type boat, then chances are it a a very different prop on it than what would be needed for that much lighter aluminum flat bottom hull. I'd consult a prop guru and run it all by them to see what they say before I began major hull mods. Much easier to swap out props.

Nice rig though. I appreciate some outside the box engineering.

although I don't agree - - - - I am interested in the modification.

Could you expand a little on how you will make it ?
all sheetmetal or plastic insert ?
welded or riveted ?

Just curious as I have never heard of it before.

I flipped the boat over and started on the mod. I am using Styrofoam to form a pad 14" wide and 4" tall x 8' long down the center then 2" tall strakes next to the pad then taper down to the hull. I will fiberglass everything in. Pics will come soon.

Sounds like a pretty ambitious project. How long you think it will take?
I love construction and modifications. Especially with fiberglass.
Looking forward to the tour. Please do the photos.

I hope, in my spare time, it will take about 2 weeks. I have some fiberglass experience so I know what I'm getting into. More labor than anything. We shall see.

You're finding out that a Jon has a TON of hull drag. They are stable, but stability is engineered into the hull at the (big) sacrifice of speed.

Interested in the outcome, though.

Thinking that a pad may induce more stern lift than the rest of the hull will "like". One thing that a higher performing pad hull does is to lift the entire hull out of the water, then once the boat is "on pad", the pad is the only thing in (on) the water. But it's got to have enough lift to get it up on the pad for this to happen. Bow lift mostly. Then at higher speeds, the air also helps lift the hull. Not much of aerodynamic lift happens on a jon hull. Hydrodynamic lift isn't all that impressive either. The ribs help suck it down to the water for stability.

There's ways of re-engineering it, but honestly, probably better off with a different hull to begin with.

BUT...I also like projects and I'm a watching this thread with lots of interest.