Making a Powerboat

Sounds fun to me.
Saw a little boat with that sort of construction which had a drop down ramp at the back to make it wheelchair accessible. A bit like a mini landing craft (can I do the 'it was difficult getting it up the stairs' joke? Nah...thought not) it worked a treat and the construction looked simple.
Del

What's the speed limit on the Severn - 6knots up and 8 knots down?

Watch out for those high speed boats with the flashing blue lights on the top.....

It is to go on one of the South Cerney lakes rather than on the Severn River. The speed limit on those is as fast as it will go, and considering there is a 40hp rib on the lake, my boat will not be speeding. I picked up my engine today, it is a Yamaha P65. I am not sure of the age, but I think it is 3.5hp

Bondy -- You are well advised to avail yourself of the collected wisdom of 10,000 years of human experience with boat building. This is a wheel that you shouldn't try to completely reinvent.

There is a very substantial difference between a 3 meter and a 5 meter boat. Roughly the number of adults the boat can safely carry is the length in meters minus one.

Generally any boat one meter wide even with a stable sharp chine design will be tipsy if you try to stand up in it. Raising the floor boards will worsen this tendency. My suggestion is to make it a minimum of 1.25 and preferably 1.3 meters wide (beam).

You should expect a certain amount of corrosion due to the use of steel. There are many tricks to reduce this problem.

There are lots of other factors to consider relative to how you plan to use the boat. I'll leave them for others to suggest.

Ed Weldon

Do a Google search on homemade boat plans. Most are wood, not metal. It is a little heavier than aluminum, but a lot quieter, easier to work, and you won't have to worry about leakage around the rivets.

So a steel frame with wooden panels? I will do it 4m long, because the car is 5, and it will go on the roof racks nicely then. In regards to the unstable tendency of a 1m beam, the sides will slope outwards to allow for seats, about 30cm either side.

Hi Bondy,

don't use steel, you'll just spend all the time fighting rust.

Use marine ply and wooden frames or go all aluminium.

for the joints use 3M 5200 or Sikafex 291 They both work on ally and wood.

they have adhesive capacities somewhat better than sH1t to blankets!

Chas

I would check for similar designs from Glen-L-Marine. They have just about all the designs you could want. Most are marine plywood and fiberglass, but some are metal also. They also have boat trailer plans. They sell all the plans and most of the materials. They also have videos and books. What weight capacity are you looking for? How much speed do you want? How many horsepower is your motor? I have seen narrow aluminum Jon Boats in Missouri that are close to the dimensions you are talking about. They are used by some of the resorts along Lake Taneycomo in Missouri.

Good Advice - use the tested plans of others. And do a little reading of Naval Architecture - first principles before you are the cause of a search and rescue effort.

Go all aluminum or all wood. If you enjoy working with aluminum, give it a shot. I see plenty of home made skiffs about the size your looking at or bigger made of plywood. I've never encountered anyone who made their own aluminum boat. Also FYI: I've seen used aluminum boats advertised for less then their value in scrap. It's not a cheap metal and it adds up quickly when you need so much of of it.

Also, I want to add. Make sure the transom is strong enough to handle the engine. Not sure how you'd go about doing that except overbuild it to the point where it "looks" strong enough. Do you have Mythbusters over there? They build a boat out of newspaper and ice. Then strapped on a monster outboard engine. I would have expected the transom to fold/bend with all the torque that would have been applied. It worked fine until it began to melt.

I am going for Birch Plywood, about half a centimetre thick because it is reasonably light, and quite strong. I was looking at some on an old boat that is there today, it is only starting to break now after at least a decade. I think a steel frame would be good because it would provide rigidity. As long as it is coated, it should be ok; right? Obviously I will also coat the wood because it is expensive. The Outboard is a Yamaha P65 3.5hp engine. I presume it is 65CC? It is 2 stroke, and has no gears - you turn it round to reverse. I haven't got it started yet, but will keep trying. It apparently does work. With the steel, they are cutting up some old boat trailers soon, so I can get some of it then.

Bondy -- Now that you are getting into details I'd suggest you just forget about the steel and make the entire boat out of plywood. No reason why the plywood can't serve two functions; that is, both structural rigidity and basic hull form, rather than just the hull form. You might have to jump a couple of millimeters in plywood thickness; but the weight savings will be substantial and the corrosion issues will go away.

Look into modern "stitch and glue" designs where sides and bottom are designed to be cut to a very specifically designed pattern. Then they are temporarily bent and fastened edge to edge with wire "stitches" laced throught small predrilled holes much analogous to the way an old-fashioned shoemaker cuts, bends and stitches flat pieces of leather to make a shoe. In the case of the boat building process these laced seams are then covered with strips of fiberglass and resin to reinforce the joint and seal up the leaks. Seats provide lateral bracing and a transome cut from thicker plywood is fitted with appropriate corner bracing. Keel, gunwale and stem pieces are fitted according to the design to provide local structural requirements.

Plans for stitch and glue designs are readily available here in the USA for moderate prices.

Remember the lighter you can make the boat (consistent with the "bigness" of the water you intend to launch into) the easier it will be to deal with on and off the top of your vehicle. This is especially the case where you may not have the company of another strong adult for your boating activities. Here in the USA it is common to see 12 foot "cartopper" boats with two small pneumatic tires such as might be used on a wheelbarrow fitted temporarily on rigid brackets to a boat's transomme. This facillitates movement over soft and uneven ground at unimproved launching locations.

Ed Weldon

Thanks. I have found some Birch Ply, for about £10/SQM. Its 6.5mm thick, and I have shortened the boat by a meter, just to save an extra £20. Im not sure the engine would have coped with it anyway. I could have a wooden frame, and just re-inforce the rear plate with a bit of Steel.

A friend of mine is making a real power-boat. http://www.chelseacoachworks.com/

I saw that somebody posted a reference to Glen-L; from what I have been told, I would certainly recommend you check out their site.

Cheers. I have checked the site out. The only thing is I am going for a flat hull, whereas the GLEN-L is a Vee hull, and has an inboard engine. Also, I am going for an open topped boat.