new pontoon owner

[cds11]

hi, I recently bought a 1993 sweetwater 24 ft pontoon without an engine on it. I also recently bought a 2000 Johnson 70 hp and put on it. everything seemed fine with just me and my wife on it but when more people and more weight it really struggles and uses a lot of fuel. I did some research and found that the motor is supposed to be installed with the cavitation plate even with the boats transom. I didn't know this when installing the motor and put it down as far as it would go which is about 6 inches below the transom as the motor is a long shaft. what negative effects will there be having the motor this low? I plan on raising it up soon but just wanted to know what problems it would cause? thx, chris

 

[HotTommy]

The main effect on performance is that you are dragging an extra 6" of engine leg through the water and that will impact speed and fuel economy some. But I doubt it is the main reason your boat struggles. 70 HP is not much for a 24' pontoon boat. You likely have to run near full throtlle to get a good breeze and that means you will likely be burning about 7 gallons per hour.

 

[jbcurt00]

I'd also bet the struggling 70hp is a bigger problem then the extra 6in of leg in the water

 

[ahicks]

If your engine is equipped with a prop sized for a runabout/fishing boat, and not sized specifically for use with a pontoon boat, it would act pretty much as you describe. The easiest way to know for sure is to know what rpm's the engine is turning at wide open throttle. You can compare that info to what the engine should be turning, and also to select the correct size.

 

[MaPaHa]

I agree with everything that's been said, especially about the prop. The best you can hope for is to get a good prop on it and you'll have to have a tach to start that process. There are several types of props you can go with for pontoon boats but the need is different than a bass boat or runabout. I run a 4 blade "off shore" prop with large blades but I'm running a Tri-toon with a 150 hp. If you can locate a good prop shop that understands pontoons and helps select one for that boat would be nice. If you don't have a tach there's not much that can be done except pick one based on experience. There's some prop calculators on the internet that you could start with. Overall, if you're new to pontoons, you're not going to go very fast with a 70 hp on a 24 foot pontoon with a load. Under skirting will help some especially if you feel surges of water hitting the underside of the boat under a load and rough water. Look at the sides towards the back while you're running and see if water is gushing out between the top of the toon and railing. If so, water is hitting the joist and slowing you down. You might get a mph out of setting the motor higher and a mph or two from the right prop and a mph or two from under skinning the bottom. What speed are you running from a gps? Run the prop calculator and see what it says.

 

[Illinoid]

My Toon was a 24 with an old 70 Johnson. I worked every year to improve speed, bigger gains at first and smaller as time went on. There are lot of things to play with, Prop, Trim, throttle adjustments, engine height, underskinning, weight distribution, cleaning toons and bimini adjustment. It was a challenge and a lot of fun to figure things out but always 2 steps forward, and only one step back if I was lucky.

 

[cds11]

thanks for all the replies everyone. I tried moving the engine up but it didn't help. I also tried going from a 14x11 prop to a 14x9 and it didn't help either so I sold the motor and I'm going to put a 115 hp on it as 115 is max rating for my toon. thx again, chris