new toon prop/rpm question

[MichaelMullis]

new toon prop/rpm question

I got ,to me, my new toon yesterday. 2000 22' crest sport with 1998 70 hp 4-stroke Johnson. The tach is not working, but I will get that fixed this week. My concern is that this boat/motor/trailer and 20 gal. gas, and 1 start battery weighted 3320 lbs. The trailer is a Venture brand, single axle, but the plate mounted on the tongue is scratched up so bad that no info can be obtained.I am estemating that trailer will be around 700 lbs which will leave me with about 2600 lbs or around 3000 lb when loaded with all gear.<br />What should my wot rpm be?<br />What prop is recommended for this situation?<br />How do I know when motor is properly trimmed?<br />The guy i bought from says he goes by the way the steering feels and by sound of motor.<br />Any info I can get will be helpfull, I will order a owners man. for both boat and motor but thought I would get a start while I wait on manuals.

 

[Silvertip]

Re: new toon prop/rpm question

Re: new toon prop/rpm question

Pontoons are not planing hulls so trimming the engine will have little if no effect. Steering feedback would provide no insight as to whether or not the prop is correct. To determine if you have the right prop you'll need a tach. Run the boat at wide open throttle varying the trim a little but probably not much from vertical. At WOT the tach should read at or very close to the maximum RPM rating for the motor. If its higher than that, its under-propped and you need to increase pitch. If its lower than the maximum its over-propped and you need to decrease pitch. 1 inch of pitch = about 150 - 200 RPM depending on prop design. When making your runs, make certain you don't trip up so much that the prop begins ventilating (blowing out) as RPM will increase and speed will drop which obviously screws up what you are trying to accomplish.

 

[BillP]

Re: new toon prop/rpm question

Re: new toon prop/rpm question

You can tell if the motor is trimmed right by the feel of the steering or if the motor cavitates. My toon is more sensitive to steer when the motor is trimmed too far down. At high speed I get best results by trimming down just enough to keep the motor from cavitating.

 

[MichaelMullis]

Re: new toon prop/rpm question

Re: new toon prop/rpm question

Thanks guys<br /> I played with the trim a good bit on monday when I ran it. Seller said that he always trimmed up until steering got really easy then he left it alone. He also used trim to pick up bow when in heavey chop. I saw a slight increase in top speed when I was playing with trimm, but thought it more practical to use like he said to pick bow up.<br />Michael