slow to plane

[shannonlewis]

I bought an old boat
I have had it out once and loved it because it ran and I now have a boat.
It took about 10 to 15 seconds to plane which I thought was a long time. On plane it ran 4600 RPM from what I have read the range is 4200 to 4800. 4500 gave me 25 MPH on a mechanical speedo.
The boat came with two props the one I have tried is a 15x17. The other is a 14x15. I have been doing quite a bit of reading and have concluded that the other prop should plane faster but may over rev the engine if allowed. I would like to use the boat to teach my kids to ski I would appreciate any feedback or advise

The boat is a trihull 17.5 feet long
with the trailer it weighs 2800 lbs
I found a spec on the internet that said the boat weighs 1400 without engine and outdrive
it is powered by volvo penta aq 120 b and has a volvo penta 270 outdrive

 

[hwsiii]

Re: slow to plane

Shannon, if you will give me the HP of the engine and the gear ratio for the outdrive I will try and help. How many people and how much gas is normally in the boat, and what year, make and model of boat you have. Are the propellers aluminum or SS, if SS the make and model is needed.

H

 

[steelespike]

Re: slow to plane

HWSiii can hep if you can get him the info.
speaking genericallyt your speed seems slow try to get it by GPS.
Speed should be close to 40.I feel that normally the 17 would work for skiing
but I may be expecting too much from a 120. You can sure try the 15
it will get up faster but run slower and you will need to watch the rpm.
You may have a motor issue.Things to check is the throttle opening all the way?Does it have good compression,Is the bottom clean?

 

[shannonlewis]

Re: slow to plane

hwsiii
The engine is 110 hp
The reduction ratio is 2.15 to 1
normaly four people
the fuel tank holds 18 gallons so we would start the day with that
1979 corwin by enterprise E17FRIO
The propellers are aluminum
Thank you for your help

 

[hwsiii]

Re: slow to plane

Shannon, I found the boat to have an allup weight of about 3,000 pound including 4 people, gas and a base weight of about 2,100 pounds. I show you need an 18" prop to be correctly propped, but with those large surface area Volvo props evidently you can't swing that much. I would just try the 14 x 15" anyway to see what happens. But i do show a Prop slip of over 25% with the prop you have now, and that is too high in my opinion. Try the other one and give us some more numbers of RPM and speed. It depends tremendously on the blade geometry of the individual prop you are using. Here are my numbers.

Prop Slip

H

 

[steelespike]

Re: slow to plane

If the tach is reading high it may look like prop slip.See if you can verify the prop .perhaps borrow a shop tach.