boat propeller

[fordtruckin]

My work boat has a F90 Yamaha with a 13.25x17-K prop. At my elevation and full throttle, I'm getting right around 5000RPM and 30-32mph. WOT per the book is 5-6000 RPM. The issue I have is it takes forever to get up on plane. I know I will lose a bit on the top end, but if I stick around a 13-13.5" prop and went to a 13-15" pitch would that get me up on plane faster without totally killing my top end? Also, would it be worth going to a 4 blade over the factory 3 blade?

[elkhunter11]

Your acceleration will improve, and because you are only seeing 5000rpm, you may not lose any top speed.

[fordtruckin]

Would it be better to try a 13 14 or 15 pitch prop?

[Ken07AOVette]

A set of whale tails is what I would suggest first, gets you out of the hole much faster. Also if you are not running real heavy you are lugging your engine which means you are over propped. Are you able to trim up a little at fot? You need less boat in the water, which will happen when your are propped properly.
4 or 5 blade are much better for getting out quickly but you lose a little top end. A stainless prop will run much more efficiently than aluminum and not flex out. Many retailers will let you demo a prop to get the right ram, which is important. Very important, lugging a boat engine is very bad.
1- get up to proper rpm with correct prop.
2- try a whale tail if you are still taking forever to get out of the hole.
3-mess around with 4 or 5 blade props.
The issue may be hull design. Find a boat mechanic that really knows what he is talking about as opposed to a salesman looking for another sale

[elkhunter11]

If you keep the diameter of the prop the same, reducing the pitch by 1", should increase the rpm by 150-200rpm. I choose a prop that lets the engine get very close to maximum rpm, with the lightest load that I will ever have in the boat, that way it will still be in the recommended rpm range with the heaviest load.

[fordtruckin]

Originally Posted by Ken07AOVette

A set of whale tails is what I would suggest first, gets you out of the hole much faster. Also if you are not running real heavy you are lugging your engine which means you are over propped. Are you able to trim up a little at fot? You need less boat in the water, which will happen when your are propped properly.
4 or 5 blade are much better for getting out quickly but you lose a little top end. A stainless prop will run much more efficiently than aluminum and not flex out. Many retailers will let you demo a prop to get the right ram, which is important. Very important, lugging a boat engine is very bad.
1- get up to proper rpm with correct prop.
2- try a whale tail if you are still taking forever to get out of the hole.
3-mess around with 4 or 5 blade props.
The issue may be hull design. Find a boat mechanic that really knows what he is talking about as opposed to a salesman looking for another sale

Brand new boat last year. Funny when I was talking to the dealer last year I had it winterized at, he didn't seem very interested in making a sale for a prop etc... Just said it sounded like the engine wasn't developing full power because of the pitch and left it at that. I will admit I'm learning as I go with boats. Never been around them much outside of work.

[Ken07AOVette]

Originally Posted by fordtruckin

Brand new boat last year. Funny when I was talking to the dealer last year I had it winterized at, he didn't seem very interested in making a sale for a prop etc... Just said it sounded like the engine wasn't developing full power because of the pitch and left it at that. I will admit I'm learning as I go with boats. Never been around them much outside of work.

Maybe he was waiting for you to damage the engine lugging it, so he could get commission on a new mill. And no, not covered by warranty. All the new engines have digital ECM which shows how it was run.
Slick little deal for diagnosing issues but also works against you if you do not know certain things like overloading the engine aka lugging.
I know that's a stretch but...

[fordtruckin]

Originally Posted by Ken07AOVette

Maybe he was waiting for you to damage the engine lugging it, so he could get commission on a new mill. And no, not covered by warranty. All the new engines have digital ECM which shows how it was run.
Slick little deal for diagnosing issues but also works against you if you do not know certain things like overloading the engine aka lugging.
I know that's a stretch but...

Ha I work for the government. They would use lowest bidder if they had to repower.

[elkhunter11]

Assuming the 5000rpm was with the lightest load the boat will normally see, you are 1000rpm below the maximum recommended rpm range, so I would likely drop the pitch by 4" , hoping to end up close to 5800rpm. That will allow the engine to make maximum power, and get you up on plane much quicker, without risking exceeding the recommended maximum rpm. And if you do add more load, you should still be well within the recommended operating range.

[Positrac]

Originally Posted by elkhunter11

If you keep the diameter of the prop the same, reducing the pitch by 1", should increase the rpm by 150-200rpm. I choose a prop that lets the engine get very close to maximum rpm, with the lightest load that I will ever have in the boat, that way it will still be in the recommended rpm range with the heaviest load.

This is good info.

OP, I’d shoot for a 14” if keeping to a prop with the same characteristics. If you have aluminum and we’re going to a stainless prop I’d go 15”. But, in the end it is trial and error a bit because you are so far away from max rpm at wot.

[Buckhead]

Originally Posted by fordtruckin

My work boat has a F90 Yamaha with a 13.25x17-K prop. At my elevation and full throttle, I'm getting right around 5000RPM and 30-32mph. WOT per the book is 5-6000 RPM. The issue I have is it takes forever to get up on plane. I know I will lose a bit on the top end, but if I stick around a 13-13.5" prop and went to a 13-15" pitch would that get me up on plane faster without totally killing my top end? Also, would it be worth going to a 4 blade over the factory 3 blade?

A 14 pitch with the same diameter will get you a lot closer to where you want to be. 3 or 4 blade would work just as well. A good 4 blade stainless is going to give you a bit more holeshot and better handling and bite in the mid range than an aluminum 3 blade. A good 3 blade will give you a couple mph better top speed. I prefer a stainless 4 blade for good overall performance myself - I don't care that much about top speed.
If you really want the best holeshot and mid range performance then a 13 pitch will get you there, but you might have to watch that you don't over rev at WOT. That is how I prop my fishing boats so I get the best performance in the mid range both for rough water use and better handling if I want to troll with the main motor.
You aren't going to lose any top speed either way and may even gain a bit as your boat is over propped the way it is set up now.

[Coiloil37]

You need to post more information before any educated opinions can be given. At this point it’s all guesses…

What boat?
Are you trimming the motor all the way down when you take off and do you trim it up once your on plane? If so, how far have you trimmed it up? Until it starts to ventilate or something else?
Post a picture of the motor trimmed down where we can see the position of the anti ventilation plate relative to the bottom of the hull.

For far less likely possibilities;

Any reason to suspect a faulty reading tach?
Did the boat perform the same last year?
Does the boat seem to be running correctly and not suffering from any mechanical or fuel issues?

[Buckhead]

There is plenty of information in the OPs post to provide educated and experienced recommendations.
It's a workboat, so its going to be on the heavier side. Also, means it's its probably being used daily so the OP knows how to run it.
It's a 90 HP 4 stroke so it's going to lack a bit of bottom end torque, and running a 17 pitch prop, at altitude. The OP is not at sea level, so is not going to see the full 90 HP. It is clearly overpropped.
It's not rocket science.

[Walleyedude]

I’m with Coiloil37.

The more information you can supply, and the better that information is, the closer I can get you with an exact recommendation or options for a prop. The old saying “garbage in, garbage out” holds true.

Going from a 17” to a 14” pitch prop is a drastic change, and there’s so many more factors that go into selecting the right prop other than simply pitch.

I’m also not a fan of “whale tails”. They’re a band aid in my opinion. If your boat weight distribution, motor height and prop are setup correctly, they’re more likely to hurt performance than help it.

[Coiloil37]

Originally Posted by Buckhead

There is plenty of information in the OPs post to provide educated and experienced recommendations.
It's a workboat, so its going to be on the heavier side. Also, means it's its probably being used daily so the OP knows how to run it.
It's a 90 HP 4 stroke so it's going to lack a bit of bottom end torque, and running a 17 pitch prop, at altitude. The OP is not at sea level, so is not going to see the full 90 HP. It is clearly overpropped.
It's not rocket science.

That’s funny. Nothin like doubling down…

Chances are he is over propped but that can’t be confirmed with the information given. If your original “guess” proves to be correct that would make it lucky, not informed.

Need to know the boat, how it was loaded or perhaps it’s weight (if known). How high the engine is mounted on the transom and how the man on the controls is driving it. Pretty simple stuff

[fordtruckin]

Originally Posted by Coiloil37

You need to post more information before any educated opinions can be given. At this point it’s all guesses…

What boat?
Are you trimming the motor all the way down when you take off and do you trim it up once your on plane? If so, how far have you trimmed it up? Until it starts to ventilate or something else?
Post a picture of the motor trimmed down where we can see the position of the anti ventilation plate relative to the bottom of the hull.

For far less likely possibilities;

Any reason to suspect a faulty reading tach?
Did the boat perform the same last year?
Does the boat seem to be running correctly and not suffering from any mechanical or fuel issues?

Brand new boat as of last year so 2021 with a 2021 Yamaha f90. Has 18.4 hours on the engine. Boat is an all aluminum 18’ Stanley Mink center console. Boat runs with 1 or 2 people on board other than that it’s just a few personal items and life jackets, tow ropes for Disabled boats, various paper regulations. Work stuff but less than 20# total.

Boat engine is running correctly just takes forever to get up on plane at full throttle. Once on plane it handles like a dream. Start out trimmed all the way down and slowly bring the trim up as the boat starts to move. If I leave the trim all the way down the bow rises and you get no speed. Cant trim too high as the boat will porpoise significantly and not get up to speed. I’d say on the gauge when running at cruise the trim is about neutral maybe down a bit. I go off the feel of the boat sound of the engine and then check the gauge. I know a 115 would be much better for this craft but as it’s a govt boat they do the minimum rating of 90hp.

https://stanleyboats.ca/boat/mink/

[elkhunter11]

Originally Posted by fordtruckin

Brand new boat as of last year so 2021 with a 2021 Yamaha f90. Has 18.4 hours on the engine. Boat is an all aluminum 18’ Stanley Mink center console. Boat runs with 1 or 2 people on board other than that it’s just a few personal items and life jackets, tow ropes for Disabled boats, various paper regulations. Work stuff but less than 20# total.

Boat engine is running correctly just takes forever to get up on plane at full throttle. Once on plane it handles like a dream. Start out trimmed all the way down and slowly bring the trim up as the boat starts to move. If I leave the trim all the way down the bow rises and you get no speed. Cant trim too high as the boat will porpoise significantly and not get up to speed. I’d say on the gauge when running at cruise the trim is about neutral maybe down a bit. I go off the feel of the boat sound of the engine and then check the gauge. I know a 115 would be much better for this craft but as it’s a govt boat they do the minimum rating of 90hp.

https://stanleyboats.ca/boat/mink/

That is not a light boat,even with only two passengers, the outboard and fuel, and just basic gear, you are pushing around 2500lbs. And you are trying to use the trim to advantage, so based on the extra information, I would still suspect that you would benefit from a prop with less pitch.

[Coiloil37]

Originally Posted by fordtruckin

Brand new boat as of last year so 2021 with a 2021 Yamaha f90. Has 18.4 hours on the engine. Boat is an all aluminum 18’ Stanley Mink center console. Boat runs with 1 or 2 people on board other than that it’s just a few personal items and life jackets, tow ropes for Disabled boats, various paper regulations. Work stuff but less than 20# total.

Boat engine is running correctly just takes forever to get up on plane at full throttle. Once on plane it handles like a dream. Start out trimmed all the way down and slowly bring the trim up as the boat starts to move. If I leave the trim all the way down the bow rises and you get no speed. Cant trim too high as the boat will porpoise significantly and not get up to speed. I’d say on the gauge when running at cruise the trim is about neutral maybe down a bit. I go off the feel of the boat sound of the engine and then check the gauge. I know a 115 would be much better for this craft but as it’s a govt boat they do the minimum rating of 90hp.

https://stanleyboats.ca/boat/mink/

I think what I’m interpreting is that if you leave the outboard trimmed down the boat won’t climb over it’s bow wave. Is that correct? So your trimming up a bit to lift some of the bow out of the water which allows you to get on plane and over the wake?
That boat was rated for a max of 90hp until a few years ago when they increased the max hp to 90. Your at the min recommended hp but it’s not THAT bad.
Your not all that heavy.
Porpoising is never good, likely a weight distribution problem that should be addressed because until you can trim the boat out properly you’ll never know it’s potential with the prop your running now.
If you can’t trim up very far your never going to hit max rpm unless your extremely under propped. On my boat I’ll hit 6100 rpm on calm seas, flat stick just prior to the prop ventilating. If I leave the engine trimmed down I see about 5300 rpm.

Still need to see how low the engine is on the transom. My gut says it’s probably to low. A picture would help. The other alternative is in this thread.

https://www.suzukioutboardforum.com/...the-right-prop

[Unregistered user]

A brand new aluminum prop from Propmasters in Airdrie is $200, they also really know their stuff. Call them tell them what's going on and they will get you set up right.

[fordtruckin]

Originally Posted by Coiloil37

You need to post more information before any educated opinions can be given. At this point it’s all guesses…

What boat?
Are you trimming the motor all the way down when you take off and do you trim it up once your on plane? If so, how far have you trimmed it up? Until it starts to ventilate or something else?
Post a picture of the motor trimmed down where we can see the position of the anti ventilation plate relative to the bottom of the hull.

For far less likely possibilities;

Any reason to suspect a faulty reading tach?
Did the boat perform the same last year?
Does the boat seem to be running correctly and not suffering from any mechanical or fuel issues?

Tried to post a picture of the engine and hill but it won’t cooperate. Anti ventilation plate is about 2” above the keel.

[EZM]

Originally Posted by fordtruckin

Tried to post a picture of the engine and hill but it won’t cooperate. Anti ventilation plate is about 2” above the keel.

I've messed around and changed up many many boats and have learned things the hard way and finally feel like I am starting to know a little about how to set a boat up for optimized hole shot (and control) as well as top end.

What I learned is ... Ideally, [B]the cavitation plate should be in line with the bottom of keel with a conventional hull when at 90 degrees. 2" seems a little high. Usually I set mine within 1/4" below/above the hull.

If I were in your shoes I'd try and drop it a couple holes (assuming you can) and take it for a spin.

Adjustments to pitch prop / design / etc... should be done from neutral - cavitation plate in alignment with bottom of keel. If your cavitation plate is behind the boat and it's not pushing clean water down - you are not getting a bite and its impacting your hole shot AND your top end (although less trimming up is likely to reach max speed for you). Easy to test and play with this on a clam water day, full out, and playing with trim to see where she cruises fastest.

As mentioned, many other factors here, but based on your boat, and what you described, I'd start there - it's a little elbow grease and doesn't cost you anything.

If it's still not giving you the hole shot you want, then pitch down a few degrees BUT I BET DOLLARS TO DOUGHNUTS if you are 2" high - this will solve most of your problem as you described it without having to swap props.

That's where I'd start anyways.

[Coiloil37]

With that information I would do the dynamic test as outlined in that link I provided to see where the anti ventilation plate is when your on plane.

I initially expected the donk would of been mounted to low and be creating to much drag and not let the outboard hit max rpm.

Mounted to high can reduce bite and fail to give you a decent hole shot if it’s not in clean water. However, it should have also resulted in hitting your rev limiter from that same lack of bite, which it’s not… So I would check it while underway.

Either way, confirm or correct the engine height first then move on from there.

If it were mine I would also be working on that porpoising issue but I would fix one thing at a time.

[fordtruckin]

Originally Posted by Coiloil37

With that information I would do the dynamic test as outlined in that link I provided to see where the anti ventilation plate is when your on plane.

I initially expected the donk would of been mounted to low and be creating to much drag and not let the outboard hit max rpm.

Mounted to high can reduce bite and fail to give you a decent hole shot if it’s not in clean water. However, it should have also resulted in hitting your rev limiter from that same lack of bite, which it’s not… So I would check it while underway.

Either way, confirm or correct the engine height first then move on from there.

If it were mine I would also be working on that porpoising issue but I would fix one thing at a time.

Depending if the weather holds I plan to get out and test the motor tomorrow. Stay tuned!

[fordtruckin]

Well took a coworker out who grew up running boats and spent a few years in the Navy out to see what he thought. Best we could get trimmed out was 5200rpm and 32mph. Still took a long time to get up on plane. The anti-ventilation plate was about 2" above the surface of the water when trimmed out and on plane. The lake was not calm as a storm was brewing, maybe 1' waves. Will try and get the new prop installed this week and see how that does. Going from a 13.25x17 to a 13.5x15. In the meantime, is it relatively easy to install your own electronics or is it better to have someone do it for me? I got a Helix 10 on the way. Very shocked work gave me the ok to buy it!

[Buckhead]

Originally Posted by fordtruckin

Well took a coworker out who grew up running boats and spent a few years in the Navy out to see what he thought. Best we could get trimmed out was 5200rpm and 32mph. Still took a long time to get up on plane. The anti-ventilation plate was about 2" above the surface of the water when trimmed out and on plane. The lake was not calm as a storm was brewing, maybe 1' waves. Will try and get the new prop installed this week and see how that does. Going from a 13.25x17 to a 13.5x15. In the meantime, is it relatively easy to install your own electronics or is it better to have someone do it for me? I got a Helix 10 on the way. Very shocked work gave me the ok to buy it!

I think what you are seeing there is the anti-splash plate. The anti-ventilation plate is directly above the prop. If the anti-ventilation plate was 2" above the water the prop would be pulling in so much air the motor would be right up against the rev limiter all the time. A 3 blade aluminum would probably not grip at that height. That is what the anti-ventilation plate is there to prevent - the prop from grabbing air and you want it more or less level with the water surface or just slightly below where it is skimming on top of clean water.
It is a common misnomer for a lot of boaters to call it the anti-cavitation plate. Cavitation is a completely different issue and is the actual boiling or turbulence of water on the prop blades themselves.