prop depth on mini pontoon

[SGordo]

I have never owned a boat, and I need Help!
I have built a mini pontoon boat with a 6hp Johnson that breaks down and fits in my Honda CRV.
I am not sure as to how deep the prop should be. I read that the cavataion plate should be even with the bottom of keel, I have it set that way but since motor is between pontoons there is no keel in front of the motor.
Everything worked out well on maiden voage but I seem to get no difference in speed from half throttle to full throttle. (Just more noise!) The motor does seem to want to throw water onto the pontoons as the motor sits between the pontoons in the back.
I don't expect to see great speed from 6hp, but just wondering if prop is too0 high? too low? or do I need to add a pan like the transom pans on large pontoon boats?
Any suggestions would be greatly appreciated!

 

[mr 88]

Your hull is basically a displacement style and will not go any faster with a 30 hp or 6 . So you giving it more throttle is not going to give you more speed . In theory of you take a line and run it from one toon to the other on the very bottom of them ,that is where your cavitation plate should be . Not going to make any difference in your case as long as the water pick up is in the water. You would need to put flat plates on the back of each toon with a bigger motor to get it up on a plain . Way touch drag in your set up .

 

[SGordo]

Thanks for your help. I just wanted something to cruise the lake, so I'm not dissapointed with speed I am getting. The caviation plate is currently right where you suggested. I chose the 6hp for easy of transport and putting off and on.
Thanks again.

 

[airshot]

Kind off a cool little boat there !!!

 

[dwco5051]

Looks like a fun boat to tool around in. Nice job.

 

[SGordo]

Kind off a cool little boat there !!!

Thanks, it was a fun build and pretty satisfying when all went as planned.

 

[SGordo]

Looks like a fun boat to tool around in. Nice job.

Thanks, now on to painting now that I know it floats!

 

[ahicks]

Is there a way you could easily TRY it with the motor moved down an inch or 2 to see what happens?

 

[SGordo]

Is there a way you could easily TRY it with the motor moved down an inch or 2 to see what happens?

Yes, I can build another transom that would lower the motor since they bolt off/on. I think I will try it since according to the formula of hull speed at square root of 8.5’ length times 1.34 = 3.9 mph, I am currently seeing 7mph with one aboard. Also hope to not see so much water thrown up on back section of pontoons. Although this happens mostly with two on board.
thanks, I’ll post results.

 

[airshot]

Having many boats over many years, some boats just throw up more water than others do. Shape of hull, length of motor leg, distance motor is from transom etc. Lots of factors. My current Sylvan throws up more than my other small boats until you run above 25 mph.

 

[aspeck]

Definitely a cool little boat. Did you find it difficult to get it registered by your states governing body?

 

[Beagleville]

Very cool. Looks like a home built version of a CraigCat.

 

[SGordo]

Definitely a cool little boat. Did you find it difficult to get it registered by your states governing body?

No, it was very easy to register in Ohio.

 

[SGordo]

Very cool. Looks like a home built version of a CraigCat.

I’ll admit that design was the basis, I just wanted to be able to transport in my car with no storage or trailer costs.

 

[SGordo]

I’ll admit that design was the basis, I just wanted to be able to transport in my car with no storage or trailer costs.

 

[Beagleville]

Very impressive design, particularly where the whole thing knocks down to fit in the car. I'll bet it's a lot of fun. Well done.

 

[SGordo]

Very impressive design, particularly where the whole thing knocks down to fit in the car. I'll bet it's a lot of fun. Well done.

Thanks, it’s a lot of fun.