Prop help for Yamaha F90 please!

Hi!

2006 Alumacraft Navigator 165cs (17 foot) rated for 90hp max, running 2006 F90 Yamaha.

Stock prop is 13-1/4 x 17.

Average load is 2 people, 10 gallons of gas and around 300lbs of batteries, gear, trolling motor, etc.

I was getting around 5800-6000 WOT with stock prop, top speed GPS of 33-34, but would lose bite when even cornering slightly when trimmed, typically I would trim waaaayyy down to get it to bite. It would lose bite in corners when trimmed at pretty much any cruising speed.

I just put on a Turning Point "Hustler" 13-1/4 x 17 and tried it this weekend. It rides pretty much like it's on rails now, cornering problem solved! However, it is noticeably slower out of the hole, and max RPM I get is 5200. That said, it's now GPS speed of between 36- and 37 mph (which is good I expect).

My cavitation plate is dead even with the bottom of my boat, everything seems rigged correctly. Motor is dealer serviced and very well maintained. Runs very well.

I have two questions:

1) 5200 RPM for WOT - is this good, or would I ideally like a little higher RPM?

2) Would a 15p prop (same Hustler brand) gain a few thousand RPMS wot? Would it give me better hole shot (for towing tubes)... might it even give me a little more top end?

Thanks very much!

Re: Prop help for Yamaha F90 please!

Anyone?

Re: Prop help for Yamaha F90 please!

I like the hustler prop but it is really agressive and selection is sometimes tricky.
The Hustler should allow more height try 2 holes and back off one if it vents.
You could gain both rpm and speed 2-3 mph.Perhaps a little hole shot.Some tollerate minor venting to keep max height.Then consider a prop change.A 15 would get ABOUT 400 rpm.I have also seen some very good results removing a little cup from a prop.But might be a little more venting sensitive.
See what your results are raising the motor.

Re: Prop help for Yamaha F90 please!

Spike, this is a prime example about them being erratic.



H

Re: Prop help for Yamaha F90 please!

Thank you for the reply. Just so I'm clear, is it OK to run at 5200 rpm?

Also, would (or could) a 15p give me approx the same RPM and MPH as raising the motor? I'm not adverse to raising the motor, but am totally not adverse to switching the prop also... the dealer that sold it to me is willing to exchange...

Re: Prop help for Yamaha F90 please!

I don't know the rated rpm of your motor but I would guess it is closer to 6,000.
Generally a 4 stroke needs to be set up to run near te top of its rpm rating.
The closer your result is to that the better your performance will be.
Assuming you can gain ABOUT 400 rpm with a 15 you would be at 5,600.
You'll have to find out your max rpm rating to know if 5,600 is ok.
You will still likely be dragging too much motor through the water wasting hp.
and performance.As I suggested raising the motor could result in both an rpm and speed improvement.All this improvement will result in improved fuel use.
At 9gph(gallons per hour) @ wot (wide open throttle)I would think that is a nice result.

Re: Prop help for Yamaha F90 please!

Great, thank you... making arrangements to get my motor lifted two holes today, will report on results.

Cheers

-Scott

Re: Prop help for Yamaha F90 please!

yamaha website say 5 to 6 thou. rpm.whats wrong w/ 5600?

Re: Prop help for Yamaha F90 please!

OK, tried it this weekend with the motor raised one hole. The RPM remained virtually unchanged @5200, as did hole shot. I'm quite certain that the hole shot with this 17p Hustler isn't going to work for towing the kids around.

I would say that handling was worse, it seemed like I could trim it less before it cavitation and would start to blow out on turns. Also, average top speed was down about 1km.

So... is it worth trying a 15p prop? Use that for tubing? If the RPMS come up to 5600 might I see some more top speed?

Thanks again for the advice!

Re: Prop help for Yamaha F90 please!

Very unusual to raise the motor and net nothing even apparently a slght loss.
Rule of thumb says "ABOUT" 200 rpm per inch.So yes a 15 should get you "ABOUT"
400 rpm.You might consider the Solas amita 4 blade in a 15.It should solve any
venting at this height and improve your hole shot and ability to stay on plane
at less power.

Re: Prop help for Yamaha F90 please!

HEY, yamahas outboard website has performance bullitins for alumacraft boats. they have one for your boat w/ a F70,check it out!it might help you.

Re: Prop help for Yamaha F90 please!

Thank you for the replies. I find myself getting increasingly confused on a subject I had hoped would be fairly straight forward. I checked out the tech bulletins, there are similar rigs to mine running 90's that go significantly faster, even the identical boat to mine tested with the 75 ran faster!

I noticed some of these boats ran a 13" diameter prop rather than a 13-1/4... what would be the difference?

And finally - I just want know - a 15p prop - if it turns more RPM @ WOT, is it possible I could see a higher top end... or not?

Thanks

Re: Prop help for Yamaha F90 please!

Scott, Spike is very right about you need the Solas Amita 4 blade, the Hustler is not designed for pulling water toys at all.

I was getting around 5800-6000 WOT with stock prop, top speed GPS of 33-34, but would lose bite when even cornering slightly when trimmed, typically I would trim waaaayyy down to get it to bite. It would lose bite in corners when trimmed at pretty much any cruising speed.

Click to expand...

If in fact you really were getting 5800-6000 WOT with the stock prop and a top speed of 33 to 34 then you need a Solas Amita 17" 4 blade prop, and it will turn right at 200 less RPM than the original stock prop, but you will get more speed out of it.

I am basing the pitch of the Solas Amita on the RPM you quoted above (5800-6000 WOT), if those RPM are wrong then my recommendation on pitch will be wrong as well.

OK, tried it this weekend with the motor raised one hole. The RPM remained virtually unchanged @5200, as did hole shot. I'm quite certain that the hole shot with this 17p Hustler isn't going to work for towing the kids around.

Click to expand...

You are right it will NOT work well for towing anyone around.

Here is my analysis of changing to the Solas Amita, the Hustler is actually MORE pitch than the manufacturer states, as it is showing a NEGATIVE prop slip at 17" pitch and an effective prop pitch of 17.1" and that is impossible if it was a true 17" pitch, in my opinion it acts more like a bad 20" pitch with the speed and low RPM it is turning.

Prop Slip




H

Re: Prop help for Yamaha F90 please!

THANK YOU. Very, very helpful. I notice a few things in your chart that I must try and understand better... (the numbers I gave are definitely accurate):

1) So my stock yamaha prop is slipping close to 19%... is that common?

2) It seems based on the theoretical speed numbers, a 17p prop is definitely the right choice. I had great hole shot with my stock yamaha 17p, just cornering and top speed issues (apparently because of the excessive slip). If I'm correct in that assumption, would perhaps a make of 17p prop that would likely have less slip (3-blade), maybe in stainless? Give me my best all-around performance? I think I understand why you're recommending a 4-blade - because I'm harping about the hole shot with the hustler 17p, which would appear to not be acting at all like a 17p.

I'm ready to order... just would like to understand the above. Thanks again!

Re: Prop help for Yamaha F90 please!

Scott, You might try reading this for a better understanding of motor height, changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057

1) So my stock yamaha prop is slipping close to 19%... is that common?

2) It seems based on the theoretical speed numbers, a 17p prop is definitely the right choice. I had great hole shot with my stock yamaha 17p, just cornering and top speed issues (apparently because of the excessive slip). If I'm correct in that assumption, would perhaps a make of 17p prop that would likely have less slip (3-blade), maybe in stainless? Give me my best all-around performance? I think I understand why you're recommending a 4-blade - because I'm harping about the hole shot with the hustler 17p, which would appear to not be acting at all like a 17p.

Click to expand...

1) No, it is not common for smaller boats like yours, I recommend replacing the prop once you have over 15% prop slip.

2)In my opinion, the Amita will be perfect for your uses, BUT if you are willing to try a couple of stainless steel props then you will find one that will be a little faster, but the hole shot will not be as good, and the price will be much higher. You can buy the Solas Amita here at Iboats for less than $ 105.

Raise the motor one more hole and be sure to trim the motor up to maximum when you are running the Solas prop.



H

Re: Prop help for Yamaha F90 please!

Hwsiii, sent you a PM, did you receive?

Thanks all again for your help... will report on results from next step