30hp tohatsu on 16ft jon boat

[matt88]

I just purchased a 16ft by about 5.5 ft wide jon boat riveted with the high sides and was wondering about how fast my little 30hp two stroke tohatsu should push it. I had it out for the first time today and didnt have my gps on the boat but it felt like it was going maybe 15mph. Including myself and my wife and fishing gear,fuel,cooler,etc.. It had a load of maybe 500 pounds. I had that same motor on a waterlogged 11ft dell quay dory and that boat was very heavy and hard to get it on a plane but once I did get the dory to plane it would run 22mph with the same load. I know the flat bottom jon boats are not built for speed and the boat did feel light and punchy but the top end wasnt there. I also know the tri hull dory had a much faster hull design but like I said before was waterlogged and heavy. I tried all the different tilt settings and they made a minor difference but nothing major. The only other thing I can try now is to take off the doel fins. I had to take them off when the motor was on the dory as well and that made a huge improvement.It would run almost 30mph without them and a lighter load about 250 pounds. Never meant for this to be so long but should my jon run faster or does this sound right with my current motor,load,etc.. thanks in advance also the cavitation plate is set even with the bottom of the boat,thanks.

 

[Whoopbass]

Re: 30hp tohatsu on 16ft jon boat

I've seen similar set ups run much faster then 15 mph.
Run it by yourself with no load and see what it does and go from there.
Maybe a lower pitched prop would help when you have a heavy load.

 

[matt88]

Re: 30hp tohatsu on 16ft jon boat

I think your probably right because it doesnt rev as high as it did on the other boat when I had it planed out. The only problem is I cannot find a prop for my engine its an 1982 30hp tohatsu and I think nobody manufactures a lot of parts for these engines anymore,but maybe I can tweak it. I have another question also. When I mounted this engine I set the cavitation plate even with the bottom of the boat but when I tilt the engine in the last two tilt settings there is slippage in the prop that is kinda off and on like when it tries to plane out the prop is too high. On a jon boat should the cavitation plate be below the bottom of the boat an inch or two?

 

[pvanv]

Re: 30hp tohatsu on 16ft jon boat

You may need a different prop for your load. I see a lot of them (7, ranging in pitch from 14.2 to 8.3) on the chart at http://www.tohatsu.com/accessories/prop.html

If the prop is ventilating out of the water, you will need to go deeper. Or, you may have a damaged/slipping rubber hub causing both problems.

 

[Wee Hooker]

Re: 30hp tohatsu on 16ft jon boat

I've got a heavier but still 30 hp (Nissan) 4 stroke on a 16'x6 aluminum V hull. With a 440# base weight, two batteries, full (30gal livewell) and two guys with gear, I get jsut over 28mph on teh gps with a 10P prop. That jon should be flying IMHO. My guess is you have engine troubles.

 

[matt88]

Re: 30hp tohatsu on 16ft jon boat

Engine trouble is a possibility because even though it runs smooth and seems to have power it is an old engine that I have been trying to work the quirks out of since I purchased it. The compression is good (about 120 on both cylinders and I have had carb troubles,fuel pump troubles and in the beginning with this motor the water valley was clogged and was overheating. I have since fixed all these problems but another problem would not be out of the question with my experience. As for the prop it was bent every which way when I got the motor and I layed it on some round tube and beat it back straight and cupped it the best I could. Im sure this is robbing a lot from me but I didnt think it would be that much. Although it wouldnt even plane out the small boat I had until I tried to rework it. Today I dropped the motor about 2 1/2 inches below the transom and I havent been able to try it yet because its pouring the rain but Im pretty sure my prop will have to be reworked by someone who can balance it,etc,etc, and knows what they are doing,lol. Thanks a bunch for telling me what your jon runs with the similar setup though. I finally have an idea of what it should be doing and realize I still have some problems to hash through. Any other info is much appreciated and thanks again.

 

[matt88]

Re: 30hp tohatsu on 16ft jon boat

I finally remembered to bring the gps on the boat with me last night and by myself it ran 22mph. That is also the fastest number I saw on the other boat when I had it on the gps. Im not for sure but I think my prop is limiting me to this speed. I will probably try to rework it again but I think I will have to send it off to have it done right. Does anyone have any tips on reworking a prop? thanks. Also,lowering the motor did take care of my slippage problem.