Need help with prop selection

[richve]

Gentlemen I need your help with a prop question.Yesterday I took the wife for our first outing since purchasing a 1991 Maxum 1700XR with a 1991 Force 70 HP model 708A91B.The motor idles and runs good. Fresh gas. The best I could do was 4500 RPM and 30MPH on the boat speedometer at WOT. I don't know if this is the original prop as I am the third owner. Prop 48 816706 A40 14P. We had a full tank of gas-12 gal. battery,one anchor,and less than 20 lbs. of gear. My wife and I together weigh about 300 lbs. iboats site lists boat at 16.58 ft. long and weighs 1305 lbs. without any gear or fuel. Motor weighs 212 lbs. Operating range 4500 to 5500 RPM. This prop is aluminum.

Maintenance since purchase:new water pump,sparkplugs,thermostat,Racor,rebuilt carb,rebuilt fuel pump,replaced all fuel lines-Trident A1. Compression test 120,120,125. Decarb with Seafoam. Should I buy a 12 inch pitch prop or even a 4 blade prop. On our vacation this summer my son and daughter want to do some tubing. How will this influence my prop choice. Thanks in advance for any suggestions.

 

[steelespike]

Re: Need help with prop selection

I would say the 70 makes you a little under powered.
Be sure the throttle plates in the carb are opening all the way.See if it responds if you tickle the choke.Be sure the stator advances as it should.
Is the prop in excellent condition?The antivent plate(just above the prop should be a little bit above the bottom of the boat.I usually suggest raising the motor to a point just before ventilation(cavitation) becomes a problem.We need to know these things are right in order to be sure you need a prop change.Probably will end up suggesting a 12" 4 blade solas amita prop. Assuming you can find one.

 

[steelespike]

Re: Need help with prop selection

Did a little research it appears you won't find a 4 blade unless you look farther than I did.Dropping to a 12" or maybe an 11will help.But try to check these other things first.
Weight distribution will be critical when tubing etc.You also may want to consider something like smart tabs.Also motor trim ,trim in for better hole shot.

 

[richve]

Re: Need help with prop selection

Steelespike,Thank You for the info. The boat is rated at 75 HP max. I will certainly checkout all your suggestions when I return home. Spending the weekend at my son's place in Virginia.Thank You Very Much for the response.