Motorcycle powered hydro

I'm planning on building a small (around 12 ft) hydro boat powered by about a 1000cc motorcycle engine.
I saw one done by stupidbaker57 when I was researching for it and now I'm a member of this site.
Here are some basic pictures about what the hull is going to look like. Anyone see any major design flaws?
Remember it's only a basic drawing. It will seat two people, not looking to go 1853 mph or anything just want a smaller fun cruiser for the river.

 

If you don't want to go 1853mph you don't really want a hydro. The idea behind a hydroplane is to generate a lot of lift so that most of the hull is out of the water and you are flying on a cushion of air. As a result you are very close to lifting off the water and the hull is very touchy in terms of lift and balance. There's a reason hydros are really one person boats, unless the second person is seated at the CG there is a big change in weight and balance for the second person. These hulls have a wide flat bottom that will pound like crazy on anything but a flat surface. Also, sponsons can dig into a wave top, and for that reason a pickle fork type of design is really ill suited for what you want to do.

A tunnel hull would make a lot more sense, or a padded V hull that will ride a lot softer is a better idea. Having to slow way down every time you encounter a wake or getting thrown out of the boat is as good a reason as any not to go that way. Google hydroplane crashes and youtube is full of them. Diggin a tip is the most common and when it happens it can tear a boat apart.

Just because it's fast doesn't mean it's fun. There are tons of small runabouts or tunnel hulls that would be a lot better choice than a hydro.

A one liter motorcyle engine is a lot of power for any small boat, if you really want to maranize one, think about finding a 75 hp outboard lower unit and bolting it on to that. That's a lot easier than trying to work up the claptrap that stupidbaker did. Also, for small boats you want the motor as far aft as you can get it. Hanging it off the back does a good job of that and that's why outboards are relatively fast. Putting the motor inside the boat makes it a lot harder to get the CG in the right place. Not saying you can't, it just makes it a lot harder

Finally, you ought to think long and hard about getting some plans and work from them or modify them to suit what you want to do. The design posted had a huge amount of air trapped under the nose and that's going to create a lot of bow lift at speed. If you put 80-100 hp on it, it's going to fly, literally. That's why hydros have the nose so low to the water. Putting the nose that high is going to create big problems with lift.

Look for designs that are appropriate for the power you are going to have and go from there. Not to throw cold water on the idea, it can be done, but you are jumping in at the deep end if you put a high powered engine in a hull like that.

 

Dangerous!! but i love what you thinking . Some where a couple of days back i spotted a small boat some one had done a Harley vee twin and coupled it to a stern drive , its reall neat looking !! any one else seen the pictures ??
I would take the ned step and graduate to a tunnel as has been suggested already . its a better boat and for more than one person a safer choice as well . go chat to the aeromarine guys about your ideas they have the tunnel thing sorted well and truely .
http://www.aeromarineresearch.com/stbd2.html
I think youll like this place !!

 

My first idea was to do a pickle fork/tunnel type thing. I don't really want to go with a V hull because frankly, I think they look lame. I am in love with the pickle fork/tunnel/hydro/cat look so I want to do something of that sort.
My first idea was to do the picklefork tunnel but I wasn't sure how to do the drive system. That's another thing is I don't really want to go buy an outboard. I would rather put together a "claptrap" deal like stupidbaker did than buy an outboard. To get the engine as far back as possible I'll have the motor drive come out the front and gear it to redirect (might have to mess with prop rotation?) out the back.

If I did go with a hydro, I would have both seats side by side just about even with the back of the sponsons.

I understand the risks of a hydro flipping but I wasn't sure if I could do a direct drive deal with a tunnel, I thought they were kinda more of an outboard deal unless you set it up with a twin drive like the offshore cats (drives coming out the back of the sponsons).

The mentioning of a sponson diving into a wave does scare me a little bit, though. I might sit back and re-think this whole deal and re-design it like a mini offshore cat (able to pound into waves.)
If I were to do a cat hull would I just have the single drive come down and out the same way as a hydro and set it up at the water line the same way?I would say the "tunnel" underneath would be about 1 ft of clearance to bottom of sponsons.

Do you think 1000cc might be too much power? I would like to go maybe 40mph, is that reasonable with about 750cc's? (I know there's a lot of variables to figure but a rough estimate would be helpful).

 

this is a rough sketch of what I'm talking about with the drive.

The problem with this would be the angle of the drive shaft coming down to meet the water line. (Unless I can put a U-joint in there to compensate?)

 

I keep thinking about it and I don't think I would get enough performance to actually get the bow to lift and flip the thing. Especially with two people sitting up front. If I did get that much performance out of it I doubt I would keep that engine in it. I would swap it out and find a smaller engine and use the bigger one for my next project. Maybe this is just me not wanting to put the hydro plans on back burner.
As far as the sponsons digging into waves I could make them taller and less flat and keep the hydro look but just have it modified for practicality and not high performance. This in turn would help with the ride be a bit smoother as well.

 

I'll redesign a boat and post pics again. Might be a few days unless I just hand sketch it.

 

If you "only" want to go 40 mph, then yes, a 1,000 is actually overkill. In fact a 750 is pretty big too. The old Merc 500 is 44 cubic inches, about 750cc and is an would easily push the kind of boat you are talkikng about easily close to 50 mph. I have a Merc 500 on a quicksilver lower unit and it can push a D class racing runabout easily over 70 mph.

I know you think V hull looks lame, but they are very successful for a darn good reason. They work. With a pad they are efficient, they handle rough water well, and they can be very fast. They also handle corners well and your speed requirements can easily be met with a monohull.

There are plans for boats like the GlennL TNT or something like that. They plenty snarky looking and can be readily converted to an inboard surface prop layout and you can move the driver back far enough to get the CG in the right place. Or start with the GlennL CD runabout and modify it to fit your motor and a two place cockpit. No matter what you do, you are probably a lot better off starting with a basic hull shape and structure that is well developed, and then mounting your motor and cockpit on that hydrodynamic layout. You stand a much greater chance of having something that you can use and enjoy with that approach than starting to sketch a hull from scratch.

If you go to a tunnel hull you are looking at probably needing to do a V drive to get the prop in the right place and proper angle, or (much easier) like I said, use an outboard midsection and gear foot and put your motor on it. I know it will cost you to have an adaptor plate made up, but it's still going to be a lot easier to do that than make an entire drive system. Outboard lower unit and mid sections for a Merc 500 complete with gear foot is likely only going to cost you $250. You will spend a lot more than that making a suitable drive system. There are some small tunnel hull mini boat around, and these can often be found for very little money if you look hard enough.

Here is a thread in Boat Racing Facts on min tunnel hull that show a couple that are not that expensive. It would be a lot easier to fix up one of these than start from scratch...

http://www.boatracingfacts.com/forums/showthread.php?t=12939

Just food for thought.

 

So are you talking about something like this?

http://www.ebay.com/itm/Mercruiser-..._Accessories_Gear&hash=item232048bf26&vxp=mtr

That might be advantageous too because it has power trim right?

I think I could get a lot more power for my $$$ if I used a salvaged motorcycle engine and attached it to an I/O unit instead of buying an outboard.
Maybe I'm looking in the wrong place for outboards but they aren't cheap around here. Unless of course I want to go with one from the 1970's and older...I already have a 1963 40HP Elgin that I fixed up and I'm just not really a fan of the whole outboard deal.

I still do want to design the boat myself instead of buy a used one.
I have lots of time for designing because I won't be building it for a while.

 

Actually I just looked up some on Craigslist. I guess they aren't too bad.. 50hp merc ~1000USD. Not too bad. I would have more time and money into dinking around with the direct drive inboard (save this for future project when I do want to go hellaciously fast).
What about that I/O drive though? good idea or just get an outboard with trim on it?

 

Make it fly !!!

Theres more to designing a tunnel boat than first meets the eye . oh yes its just two hulls BUT its the tunnels design thats the secret to the whole boat . the shape and the size and how it works . Pickle forks do you get why they are that shape ?? the early tunnels never used to be anything like that ! Maybe its just to liik pretty ??
What do you know about aerodynamics and what about hydro dynamics and surface effect !! how does surface effect work and at what speed is there a cross over from Hydrodymanics to aerodynamics . What about aerofoils a wing sections ? do you know how a wing works and what and how does it get lift , and how much lift can you get and at what speed ??. What makes hydros and tunnles flip over backwards ?? what part of the beast is the major problem the bottom or the top / or both together
Inboard motorbike engine where you going to place the motor forward or back . if you going to use a outboard what about a ex racing outboard has a better shped gear case and possible a better shape for speed . the std unit has limitations unless you are going to do some radiacal changes !
Lots to think about and cock up just one thing and you could have a dog or at least a flying poochie !!

 

The inboard/outboard you posted is heavy, big time heavy compared to what you need and want for a very small (13 ft) boat. Power trim can be rigged up very easily for small outboards. You should spend some time over on

http://www.boatracingfacts.com/forums/index.php

and on Hydroracer.net these guys are running the kind of boats you are looking at and there is a wealth of information on them and on screamandfly that would help you out and get you on the right path.

I bought a 1977 Merc 500 long shaft for $350 complete with steering and controls. I sold the controls and lower unit on ebay for $200, so I only have $150 in the powerhead. I found a mating racing Mercury 35ss complete for under $1,000. I'll put the 50 hp powerhead on the racing lower unit and the complete engine and lower unit weighs 120 pounds. That complete motor weighs less than the I/O unit you were looking at, never mind the engine.

Racing lower units aren't something that you can run every day without maintenance. In fact you should drain the oil and grease the outboard bearing after each day of use, so it's not something that you really want to mess with unless you are racing.

You have to keep your eyes open an look around, if you aren't in a hurry, look to buy the motor in the fall when folks are not wanting to store a boat or motor for the winter in your neck of the woods. If you found a short shaft outboard and put a nose cone on it to help streamline it and a low water pickup that will let you run the motor higher and let the shaft be inline with the bottom of the hull, that would be fine for a lake racer. You don't and shouldn't spend much more than $500 for a decent 50 hp merc classic from the late 70's or early 80's. Remember a lot of these engines weren't used much and although they are a bit old, you can get a decent motor with good compression and it will do everything that you want for not much money. Also a lot of folks get a pontoon boat and some of them realize that they don't need or want that big a motor, so they downsize and the motors are out there. Be patient and find something that is what you want.

Newer motors are actually heavier, and the older motors are lighter and for what you want are more desirable.

 

Well, I have a degree in applied physics and a fascination with airplanes so I know quite a bit about aerodynamics etc (at least the principles of anyway). My senior seminar in college was testing wing tips' efficiency in reducing drag caused by wing tip vortices. For this I had to build my own wind tunnel (16in x 14in throat with avg wind speed of 34 mph). So I do know a little bit about lift etc.
As far as building the boat...I am a mechanical engineer so that shouldn't be a problem.
I have also done lots of research into radio controlled boats so that might help me a little bit.
How much would a used 50HP racing outboard cost me? I don't want to dump a whole ton of money into this project either.

 

Your the kind of person id like for a neighour !!
The sterndrive thing is way to heavy and big a clunky for a small boat . the outboard leg is much more compact and tidy and lighter and a better shape .
Stern drive has a massive pump and oil tank goes inside the boat plus theres a gear box on top of the leg so add it all together the led and fittings is its probably heavyer than a complete 70 to 90 hp outboard . you been onto "Scream and fly" site ?? theres a whole bunch of crazy people on there !! all go fasts in loads of little boats . they would think your cute and you'de fit right in i reckon !!

 

Tunnels, you are spending too much time overseas. Ex-racing outboards are terribly expensive in the USA. Collectors have invaded the market and are buying up all the quicksilver towers and lower units. Racing lower units and 12 inch towers are as rare as hens teeth and twice as expensive. I lucked into mine, but that was an exceptional deal. Expect to pay at least $2500 for a 55H Merc that's a runner and not a show motor, or well over $3500 for a numbers matching nice 55H and to $4k for a 44xs motor, and then you have the Bass/Tohatsu (new) for between $5-6000. The smaller motors like the 20 hp Mercs aren't quite that bad, but 40 hp and up have taken off. A big six cylinder merc racing setup will set you back a small fortune. Sad part is that these guys are just showing them and aren't using them for anything more than a trailer queens so to me it's a bit of a waste, but that's what it is.