Author Topic: Inboard project about to start??!!  (Read 1750 times)

propellanttech

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Inboard project about to start??!!
« on: July 10, 2009, 03:23:49 AM »
Ok...so I'm new here....and haven't ever built a full size boat. I have built a bunch of other things....some wood, some not.

Here is my current plan.....I'm not necessarily looking for the most speed I can get...but would be nice if it worked out that way.

I'm going to take the HydroKart plans and build a boat. I'm not going to use the engines from the plans. I have a nice Chinese 150cc 5 speed motorcycle engine sitting here next to me. It is rated for 10hp at 8500 rpm. It is electric start which will be greatly beneficial. It will require a fuel pump (electric) but I don't see that as a problem.

The project is of course going to be a alignment nightmare because of the inboard shaft, but I'm sure I can get it done.

The only thing I am really unsure of at this point is the prop. Because the gear ratio can be changed...I'm not sure what size prop to start with....or where to get it. Shifting may happen so that could be interesting. 

If the hydro turns out to be real slow (or lacking power), I plan to put foils on it....and let if fly.

I am a glutton for punishment......as you can tell.

I think a 4 stroke with a wet header exhaust would be real cool in a small hydro. Maybe I'll get there some time soon.

J Long

propellanttech

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Re: Inboard project about to start??!!
« Reply #1 on: July 10, 2009, 06:51:36 PM »
Anyone have an opinion?

J Long

Mild Bill

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Re: Inboard project about to start??!!
« Reply #2 on: July 12, 2009, 03:19:30 AM »
HydroKart, eh?

http://www.hydrokart.com.au/

Just kidding - you probably mean the HydroKart plans available right here on the Muskoka Sea Flea site:

http://www.muskokaseaflea.ca/staticweb/index.php?option=com_content&view=article&id=61&Itemid=50

Well, I hesitate to make any recommendations because, truth be known, I don't know squat about boat propeller design. I am, however, curious that they were supposedly getting 50 mph out of the Michigan Wheel Co. 7" diameter, 10" pitch propellers mentioned in the Materials List on page 7 of the plans.

Think about it. To convert the 50 mph to feet per minute, multiply by the conversion factor 88 to get 4400 ft/min. Converting to inches per minute,  12*4400 = 52800 in/min. Now, if the propeller is nominally advancing 10" with each revolution, how many revolutions are required to go 52800"? That would be 52800/10 = 5280 rpm. Since the engines were turning faster than the propellers at the ratio 2.5:1, the engines were supposedly running at 13200 rpm, and this is for an ideal propeller without "slippage".

I suppose that's in the realm of possibility for small 2-cycle racing engines. If that sounds reasonable to you, we can take a look at a related process to arrive at an approximate pitch for your propeller.

The approach starts out simple enough. The article claims the HydroKart will go 50 mph on two 6.5 hp Power-Products kart engines from a bygone era. Since you've got 10 hp instead of a total of 13 hp, your boat will be a bit slower, say 45 mph. To convert that to inches per minute,

12 x 88 x 45 = 47520 in/min

It would probably be wise to start your experimentation with the middle gear of your transmission so you will have some leeway to go either up or down on the propeller speed. Whatever gear you pick, figure out what rpm the propeller will be turning when the engine is at full speed.  Let's say for the sake of an example calculation that it's 3600 rpm. Then the pitch would be

47520/3600 = 13.2"

Now here is where the cheese gets a little binding.  A propeller with 13.2" geometric pitch will NOT advance the boat 13.2" in one revolution because of losses that necessarily occur due to generating the thrust. (For this reason, our beleaguered little Power-Product engines would have had to be turning even faster than 13,200 rpm.)  The experts will have to chime in here, but I would guess the "slippage" is on the order of 15 to 20 percent.  Probably better to err toward the lower efficiency side, so 120% of 13.2" is roughly 16".

For your propeller speed, call it N, your approximate pitch would be  1.2 x 47520/N

If you like cheese that binds, you can indulge in some more of it by considering the propeller diameter. The Power-Products engines were turning 7" diameter propellers. The approximate pitch you would start from is pretty much independent of the engine power, but your extra 3.5 hp will probably need to be absorbed by a larger diameter or a larger total blade area or a combination of the two.  Lacking detailed information about the Michigan Wheel Co. 7" x 10" vis a vis the proposed modern propellers, we might speculate that the blade areas would be generally similar for same size diameters, so the extra power should be absorbed by increasing the diameter.  At least for airplane propellers, the torque and thrust coefficients go up by the cube and the square of the diameter, respectively.  I suspect something similar applies to boat propellers, so the diameter shouldn't be increased by too much - go up to maybe 8", certainly no more than 9".

This line of reasoning is probably all full of holes, so I've got a request for all the true experts out there:

Don't hold back on the brickbats.   :-D

propellanttech

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Re: Inboard project about to start??!!
« Reply #3 on: July 12, 2009, 04:13:32 PM »
Bill,

As I understand it....your reasoning is pretty much inline.

Now...the main question....where to get props that size. I have looked around on the internet....but can't find many props in the 6-8 in diameter range. Is everyone using custom made props?

I like your idea of using the middle gear.......

James L

boatguy

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Re: Inboard project about to start??!!
« Reply #4 on: July 13, 2009, 07:11:02 PM »
One avenue you might want to try is the Vintage Hydroplane Site which is all inboard hydros. I am in the process of getting a vintage 48cu in inboard hydro which was high points champ in 1958. These were powered by 48 cu in  Crosslely car engines--direct drive and ran 70-80mph. The boat weighed 550lbs ready to run and these guys ran all kinds of 2 blade props. Some of the later boats ran motorcycle engines before they switched to the Sunbeam Imp motors and now the Y class boats run Toyota motors.If you want to see some of the old boats, scroll down the left side to Paul Kunz photos, click on vintage and look at pics from 1960s. Any of the boats with Y on them are 48cu in hydros.My boat is Y9. I hope these guys can help you. I agree the speed figures for the Poewer Products motors seem high to me. I raced these in Go Karts and ran 8-61-64 gears with dry clutches and the oil clutches and we didnt get that speed.If I can help further, be glad to--Cheers Bill.

propellanttech

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Re: Inboard project about to start??!!
« Reply #5 on: July 13, 2009, 08:54:53 PM »
Hey...thanks for the sites to check out.

Although not exactly the same thing as I am planning to do.

Does anyone know where to get 8-9 inch props for a inboard tapered shaft?

James L

propellanttech

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Re: Inboard project about to start??!!
« Reply #6 on: July 14, 2009, 11:58:34 PM »
Thought some of the guys here would like to see the project I'm working on......not that anyone really cares....but it does keep the board alive.

This is a revised Dragonfly II. I'm working to put a water cooled 200 CC engine in it.....but haven't done all the revisions. The first engine will be a 150 cc air cooled version......mainly because I have it right here. I like redesigning for the looks, and to serve a different purpose.

The seams are not perfect yet.....takes some time to do it, and even more time to tweak the seams to be right.

This boat is allotted to have foils....which will be the last thing I put on.......also the last designed. I have a basic design for the foils. Sensor submerged single foil in the front....with piercing foils on each side in the back.

I decided that a Hydrokart would not be a good idea on the lake I frequent. I think a little deeper boat with foils is the way to go.


J Long

« Last Edit: July 15, 2009, 04:52:09 PM by propellanttech »

propellanttech

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Re: Inboard project about to start??!!
« Reply #7 on: July 21, 2009, 02:06:23 AM »
Well, I'm still working at it.

I have been talking to a hydrofoil guru (probably not a guru, but a guru by my level), and have updated the hull a little with the front foil.

The left clamp rail for some reason has disappeared in the drawing, but is still there.......who knows what is going on.

The foil will be submerged about 10 inches, with a flight height of about 10 inches. The front foil will be the steering, with a emergency hand tiller should something happen to the front foil. It does rotate back if it impacts something, hence the reason it is so far out in front. It will be attached to a bowsprit for the folding action to work.

J Long

Mild Bill

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Re: Inboard project about to start??!!
« Reply #8 on: July 21, 2009, 12:10:55 PM »
What airfoil section (er, hydrofoil section) are you contemplating?

propellanttech

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Re: Inboard project about to start??!!
« Reply #9 on: July 21, 2009, 05:21:39 PM »
Well I was going to use a NACA 0012 extrusion I found on the internet, but the guru says not to. I will probably end up with a crescent shaped foil (home cut).

J Long

Mild Bill

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Re: Inboard project about to start??!!
« Reply #10 on: July 27, 2009, 03:30:06 PM »
Which guru?

Basically, if the Reynolds number for your hydrofoil section is in the range of 1 to 6 million the NACA 0012 would theoretically be OK - maybe not ideal but workable for a knock around fun project. The Reynolds number depends on the density of the fluid, the viscosity of the fluid, the velocity of the body through the fluid, and a characteristic length (usually but not always the length of the body).

The designer of the SportFoil, a hydrofoil boat in the sea flea class, said hydrofoil sections should have a flat bottom, a circular arc top, and sharp leading and trailing edges. If I remember correctly, William D. Jackson had a similar section on his hydrofoil design that was published in Popular Mechanics many years ago. Such sections would be a dismal joke on any aircraft from a lightplane on up, but roughly similar airfoils have been used on model airplanes.

This might or might not be a clue that the Reynolds numbers for the hydrofoils on sea flea type boats are way below the Reynolds numbers for lightplanes. The way to find out would be to run some numbers - how fast are you going to go and what's the width of the candidate NACA 0012 extrusions?

I haven't perused this site very much yet, but it looks like it could be a gold mine of information:  http://www.foils.org/

propellanttech

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Re: Inboard project about to start??!!
« Reply #11 on: July 28, 2009, 01:56:30 AM »
Bill,

The guy I am talking to is a member of the foils.org site. He has been researching and building hydrofoils for quite a few years.

The NACA 0012 is a poor choice because of it's cavitating qualities. With a high load for foil area.....the 0012 foil will tend to cavitate quicker than a flat bottom ogive foil section. The chord on this extrusion is only 2.73 inches...which is on the thin side. The thickness is in line at 10%, but still the foil would be under a pretty good load.

He feels it is safer and cheaper to build a flat bottom foil...and fore go the extrusion.

My plans for the foils have not worked out. The hull length is not enough to proceed with the short hull with an inboard engine. The resulting shaft angle could cause problems with the rear ride height. So The project has been split into two different boats. One inboard (hydrokart) for the 150cc engine....and another outboard with foils. This solves the shaft angle problem.

I am currently searching for wood to build the outboard......I have secured ply for the outboard foiler, with frame material left to find. I'm going to purchase all the wood at the same time. I am only going to build one at a time (less confusion).

I should be building by this Saturday.........so the boats are becoming a reality. I figure about three weeks to construct the hull, plus another three to finish the first. I work at home.....(self employed) and have little work right now.....so I have the time to do it pretty quick.

J Long


APB

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Re: Inboard project about to start??!!
« Reply #12 on: July 28, 2009, 08:32:40 PM »
I cant wait to see the hydrofoil boat take shape. I have always had a lot of interest in that design.

i found plans for an outboard powered hydrofoil a while back i posted them in this thread but the link appears to be broken. I think i saved the PDF ona different computer so i can send them to you if you would like.
http://muskokaseaflea.ca/bb/index.php?topic=390.msg1755#msg1755

Good luck on your builds

APB

propellanttech

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Re: Inboard project about to start??!!
« Reply #13 on: July 28, 2009, 09:21:40 PM »
APB,

I have a couple of different hydrofoil designs.

The hp rating of the designs are killing me at the moment. I'm having to do a bunch of research for the design to be "legal".

I am still running down wood for building. It looks like marine plywood for the skin, and spruce for the frames.

J Long

wildwatson1

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Re: Inboard project about to start??!!
« Reply #14 on: September 02, 2009, 08:34:56 AM »
im trying to figure out how to put a riding lawn mower engine on one,the out boards are high dollar.my project-used 15 hp johnson 200 bills,drive dog repair 400 bills,throttle and gear adaptor 200 bills(which i didn't use)and for a electric starter kit its another 369.00,a 10 or 12 hp briggs with a dry clutch and a 4 sided belt would work for a lot less money and already have electric start,