What prop would have been recommended?

[TKrause]

Trying to figure if the correct prop is on drive now. Or if there is a different one recommended. Here is the info i can provide.

Looking for cruising and occasional tubing.
Currently there is a 13 3/4 x 15p Black diamond on it now. (Damaged)
4200-4600 is manufacturers recommended W.O.T. max.
Boat info is 1985 4Winns Candia 170 powered by a 1979 Mercruiser 140 (140hp)
Drive is stamped with 1:98 gear ratio
Approx boat weight by manufactures spec is 1800lbs. (however that would depend on what powerplant, i could not find an exact weight for the boat with the 140)
I have done a couple w.o.t. passes that showed 30mph + but according to my meter. (tach is inop) i was over 5000rpm. This is way unacceptable The boat is freshly tuned with timing and dwell spot on.

Again just looking to see if this prop in a brand new condition would be a correct one for this boat or if a diff. would be recommended.

Thanks in advance,
Tony

 

[steelespike]

Re: What prop would have been recommended?

In my opinion that setup wouldn't likely use a 15" pitch for anything except a boat at full load capacity trying to pull a slalom skier up on one ski. For average use probably a 19,21 or maybe even a 23" prop.Though at 23 it would probably struggle with a load.

 

[TKrause]

Re: What prop would have been recommended?

Thanks Steele, After i got it tuned and took her for a test run she just seemed like she was revving way too much especially when up on plane, the only way i could explain it would be in reference to a car with a high rear end ratio, (i.e. 4:10) she got up and went but at top end the rpm's were screaming.

 

[TKrause]

Re: What prop would have been recommended?

Ok, so i'm leaning towards the 19P or 21p, But here is my next question. at 13 3/4 my prop seems to be kind of an odd size. I thought i had read somewhere that you can go up in Dia. by a 1/2 inch without affecting the performance of your boat. What is the pro's, cons, or otherwise of going up in diameter? I realize i will have to watch the clearance on my anode when going bigger but is there anything else?

The only reason i am even looking at going up in dia. is because i seem to have a greater choice in those pitches at 14" sizes. And i'm looking at Aluminum not stainless.

 

[Philster]

Re: What prop would have been recommended?

Forget diameter. When you go up in pitch, it increases a little, especially 19p +. Still, if you see two identical pitch props from a maker and one is 1/4" smaller in diameter, get that one. If there is no difference, don't fret.

I can't imagine that engine, with that ratio and on that boat would not be able to run at least a 19. Even that seems small. 140 ponies on a 17' boat and a lot of gear reduction? W/out any math, 21p would not surprise me.

 

[TKrause]

Re: What prop would have been recommended?

Picked up the 14 1/4 x 19, Took her for a run for a few hours out on Lk. St. Clair, too choppy to open her up all the way but with the wife watching the meter it looks like i'm still going to be at around 4700+ rpm at 3/4 throttle. i'm leaning towards going back and trading the 19 for a 21. And hoping like hell that she'll still be able to get up and go when we hook a tube up to her.

 

[TKrause]

Re: What prop would have been recommended?

Ok, the numbers are in and i need a prop nut's opinion. Near glass conditions today. Had the 14 1/4 x 21 prop on. W.O.T. 6200 rpm and 33mph. cruising speed was approx 29 mph and still at 5300 rpm. speedo and gps both mirror same speed. only me in the boat and half tank of fuel (has 18 gallon fuel tank) normally there are 3 adults and a 2yr. old in the boat. Looking at my orig. post should i consider going with more pitch or stick where i'm at. In my mind i should be able to open her wide open to launch, get on plane then back off and be running around 4000 rpm tops when trimmed in conditions like today.