Prop pitch question

[Wesleyg72]

Hello everyone,

i recently bought a 97 Bayliner Capri 1950 with the 3.0 mercruiser. The prop that is currently on it I believe is a 15, if I’m reading the numbers correctly. It also came with a 17 pitch prop and I’m wondering if I’d be better off using the 17. I would normally run up and down the james River with 4 adults and at least 1 child, I’m estimating about 2925lbs all together including a full cooler and a full tank of gas. I like to run it at about 3100rpms and it reads about 32mph on the speedo. I guess the real question is would I see much of a difference with the 17 or should I just leave well enough alone?

If anyone could shed some light on this for me it would be much appreciated

 

[QBhoy]

Hi

a 15” is most likely too wee for this boat. A 17” would be considered at the small end of a prop for this even. Generally if all is original in terms of gear ratios, a 19” would be the norm and occasionally a 21” even.
The actual full numbers like gps speed, pitch and rpm etc etc will tell the tale but yeah. Get the 17” on it at least.

 

[Wesleyg72]

Qbhoy, thanks for the insight! I’ll give that 17 a try this weekend

 

[QBhoy]

Qbhoy, thanks for the insight! I’ll give that 17 a try this weekend

Good luck. Have a look at the prop on it now. I’d doubt it was a 15” at those rpms and speed. I think it would be screaming at over 30 mph.
Get the 17” on it or better still get more details and get a well suited laser 2 on her. World of difference to a boat having the right prop. Single biggest transformation a boat will see

 

[Sea Rider]

Counting already with 2 props should test both with given load on same up/down river directions at wot, check which max rpm dials each prop to see if revving inside the motor's wot rpm range factory stated. Stay witht the prop that revs at least middle to max wot rpm range. Can use the other one as a paper weight LOL!!

Once there revving between middle to max wot rpm range, can throttle at the rpm range of your particular preference.

Happy Boating

 

[Scott Danforth]

Hi

a 15” is most likely too wee for this boat. A 17” would be considered at the small end of a prop for this even. Generally if all is original in terms of gear ratios, a 19” would be the norm and occasionally a 21” even.
The actual full numbers like gps speed, pitch and rpm etc etc will tell the tale but yeah. Get the 17” on it at least.

you cant answer the OP as he has not stated the following:

what is the WOT RPM and WOT speed
what is the problem the OP is trying to correct.

the capri 19 should have a bigger motor than the 3.0 (similar boats have 4.3's and 5.0's), and at #3k its a bit for the 3.0 - so the 15p may be just right

the 3.0 is a slug of a motor, where you may need to prop for the load you want to run that day.

for my 3.0 in a smaller boat than the OP's (16'-3" and total weight of 1600#), I kept a 15p, 17p and 19p in the boat. the 15p for trolling and water skiing, the 19p for cruising (needed everyone to move forward for the hole shot) and the 17p for general use.

The OP is pushing a 19' boat that weighs 85% more than my boat did. I would expect that the 15P may be correct


Wesleyg72 go to the prop sticky labeled "Read this First" and post the answers for all the questions


https://forums.iboats.com/forum/gen...p-questions-and-topics/295058-read-this-first

 

[TunaFish389]

With the specs you gave you are running at least a 23p prop. The 15 in more than likely the diameter. I bet it's a dog, not good for the engine.

This is if tach and speedo displaying properly. You need to figure out your gear ratio, they had 1.94 and 2.0. I am not sure why they had two for the 3.0 in but sure someone more educated can.

Your max rpm should be between 4200 - 4600. If you can hit this range with said prop then one of your gauges is off.

The 17p is at the low end, a 19/21p seems to be normal. I am running the 17p and hit 33mph at 4600rpm. This just an example, my boat is old and at 5000+ elevation.

I just read above and wrong engine would make more sense.

 

[Starcraft5834]

ya.. Scott hit a line drive there... the 3.0 is a slug.. i had done on a heavy cuddy... needed a 4 blade 15p to push that heavy thing up on top of the water..... maybe this guys Bayliner is heavy.... numbers, numbers, numbers.... everyone's rig has an optimal performance given motor/weight/ hull design.... fun to think u can go faster and get better performance... if your getting optimal numbers, either drive faster on the interstate will make your boat go faster....or get a bigger motor on your boat and dont sink the rear end doing it

 

[Scott Danforth]

until the OP comes back with current WOT RPM and speed, none of us can answer his question on the prop

and a bayliner capri 19 is average weight for the size, however most boats that size have 4.3's or 5.0's and not 3.0's

 

[TunaFish389]

I disagree.. With the mph and rpms. We can estimate his prop If it's a 3.0. With 3100 rpm and 32 mph. It at or above a 23p prop all the way up to 27p. This is no matter the 1.94 or 2.0 gear ratio and going from 7% to 20% prop slip.

I think cruising speed Prop slip (only variable) is within ranges for this type of boat and load. So how can you say I can not estimate?. The only thing I can't factor in Is wrong information.

 

[jimmbo]

Until we get actual RPMs... Guestimates are just that, Guessing. Lots of wacky slip numbers appear when guessing

 

[Wesleyg72]

So I double checked the prop that’s currently mounted, it is indeed a 15p, and judging by some of the replies I’m going to take a wild guess and say the speedo is most likely wrong. I’ll check it against the gps this weekend and get back to y’all with some more info

 

[jimmbo]

Just be aware that if there is a current in water that you boat on, the GPS can be different than the speed across the water.

If the water has a current of say 5 mph you might see 30 mph in one direction and 40 mph in the opposite direction. A standard waterpressure speedo will read the same in both directions, though it might be wrong

 

[Scott Danforth]

So I double checked the prop that’s currently mounted, it is indeed a 15p, and judging by some of the replies I’m going to take a wild guess and say the speedo is most likely wrong. I’ll check it against the gps this weekend and get back to y’all with some more info

the only thing we need to know it the WOT speed and RPM. as Jimbo indicated, take the speed in both directions to account for current/wind/etc. most importantly, is that when the throttle is mashed against the stops, the motor is spinning between 4400 and 4600 RPM.

only if your motor goes significantly higher than 4600 RPM with your normal load of 4-1/2 people and gear would you go up in pitch (such as 4800-5000 RPM)

 

[Texasmark]

Glad my dog isn't in this fight. Grin

Pull up "Go-fast.com" and select Prop Slip Calculator. Once you get some numbers plug in data for everything except that for which you desire an answer. Neat thing is it lets you play around with props, especially in selecting the right pitch and see the results, keeping everything else constant......realizing that it's just a general tool, it's still been very useful to me.

 

[Sea Rider]

If you measure the speed running on both river directions at wot, will be higher down river and slower up river, consequently the wot rpm will vary acordingly, higher down and slower up river. How much will vary will depend entirely on the current speed of said river...

Happy Boating

 

[QBhoy]

Of course it’s best to get the info and put into a prop calculator but surely one can assume with knowledge of this particular boat and engine. My marina is full of these things and similar. Never have I heard of a 15” on such a set up. 17” min for pulling a skier sure. 19” would be general. Some guys even have a 21”. Ok they aren’t good in general terms.

These things with a 3.0 were the most common of them to come across to the U.K. much better with a 4.3 for sure. But it is what it is.

The bayliner, Mariah maxum etc around the 18ft mark almost overwhelmingly came with a 3.0 as standard. Certainly over here anyway.

 

[Sea Rider]

A prop calculator is good to dial a starter prop for recreational boating purposes, running at high altitudes or fast rivers or a combo of both situations it's other boating story...

Let OP try both props and check for his own which performs better running on said river. If not happy can go for a prop maximization from the one that dialed the highest wot revs and didn't reached at least middle to max wot rpm range.

Happy Boating

 

[Texasmark]

A prop calculator is good to dial a starter prop for recreational boating purposes, running at high altitudes or fast rivers or a combo of both situations it's other boating story...

Let OP try both props and check for his own which performs better running on said river. If not happy can go for a prop maximization from the one that dialed the highest wot revs and didn't reached at least middle to max wot rpm range.

Happy Boating

I use it when playing around with where you are and where you might be with a different combination. like anything else, it's all a crap shoot till you take it out and run it!