The Famous question. Which Prop is good for me!

[Deegee]

1985 thundercraft 17 foot closed bow 2100lbs dry
3.0 omc, omc outdrive.
Current prop on boat 13 1/4 x 17p.
3guys in boat with 60-80lbs of gear 3/4 tank gas, has a hydrofoil aswell on when bought boat.
turning 4100-4200rpm wot going about 35-38mph (Dash Speedo)
Sound about right or another prop you guys might suggest?
Im not looking for top end i like getting on plane quick and easy just because theres always 3 or more of us in boat.

 

[steelespike]

Re: The Famous question. Which Prop is good for me!

With a 17" prop it should be pretty peppy and possibly over reving at wot.
with one aboard. with three should be crowding max rpm if not over reving.
17 is usually used for water sports being careful to watch the revs when lightly loaded.Check throttle plates are opening all the way.Be sure the motor is in excell;ent tune.Do a compression check.Bottom clean and smooth.Prop in excellent shape.The foil will usually eatup some of your speed; something like smart tabs are a much better choice for improving hole shot and ride.A healthy 3.0 in a 17 or 18 will usually run 40+ gps with a 19 or 21" prop.
Also a 4 blade prop will improve hole shot.Let us know what you find with the motor

 

[Deegee]

Re: The Famous question. Which Prop is good for me!

havent checked the plates in carb, but pretty sure there opening. does this have to be checked out running on the lake or something that can be done in driveway? compression is 135-140 all cylinders. props not in EXCELLENT shape but its decent
smart tabs will be going on this yr sometime!
So if i go with smart tabs and that helps hole shot maybe i could step up to a 19??
i also wanna stick with al. what 3 or 4 blade should i go with?

 

[Silvertip]

Re: The Famous question. Which Prop is good for me!

Whatever hole shot you have now would likely be helped with trim tabs. But then going to a 19P prop will likely put you right back where you were. A 19P prop takes a bigger bite on the water than a 17 so it takes more power which you don't have. So you are spending money to get no benefit. Since the engine is already well below its recommended wide open throttle rpm (4600 I think) you need to investigate why. Water soaked foam perhaps? Hull design. A heavy load as you describe it. Going to a 19P prop will lower rpm even more. I would start by verifying the tach is accurate, the engine is making full power and the hull is clean and water free. The carb butterflies must be standing straight up when the throttle is full open and NO -- you don't do that with the engine running. The upper plate by the way is the choke plate, not the throttle butterflies. You may need to open the choke by hand to see the butterflies.

 

[Deegee]

Re: The Famous question. Which Prop is good for me!

Ok i will check these things out tonight after work and ill let you know.
were kinda big guys that were on it Im 6'6 310lbs and there was a 220 and 195lb guy aboard, Could be a problem!!! lol

 

[Deegee]

Re: The Famous question. Which Prop is good for me!

well foams dry carbs opening all the way BUT!!!

I changed the 13 1/4 x 17p to a 14 x 17p came with boat

the 13 i could cruise at about 25-30 at about 3100rpm max 4100rpm

the 14 i was running about 20-25 at 3500rpm max 4100rpm

the 13 needs to be fixed up the 14 is smooth. ill be putting the 13 back on as i dont think this is my rpm problem.

Today i took boat out mind you it was 100 degrees out and humid today and i notice i be at like 3/4 or little more and running 4000-4100rpm, id put it down and it sound like it wants to go more it definatly has more rpms to be had but its almost like it bogs pass 4100 and wont go farther? any thoughts what may be causing this?