Boat props x2 Help would be great!

[tmartin]

Re: Boat props x2 Help would be great!

Man, I've called three Honda OB dealerships and no one can tell me the answer to the true max rpm's before they are retarded. BUT, they did say because the rpm's (on Honda Dig gauges) are following a linear path--(steady increase to 6400) that THAT is what they're turning and all of them thought that when the cpu kicked in, they would drive the rpm's DOWN to 6000-6200. So, that makes me believe that the max rpms with my current props are 6400. (unabated) And, those motors are not reaching their zenith for the cpu to kick in. THAT rpm number, no one really knows...

Motor height is about right...they all said the issue becomes one of performance, that is, the proof of poorly hanged (too high) motors would be blow-out in turns of creating a hole in the water and cavitation. Of which, neither is happening.

So that's that.

 

[triumphrick]

Re: Boat props x2 Help would be great!

with all that weight i like the idea of 4x16's should bring u down 500. you should pick up speed with less slip. all i run is 4 blade. great hole shots. better mid range fuel econ. better for trolling. and slower on plane speed with great torque. great for fighting rough waters. my 2 cent

Me too...Ditto....my change to 4 blade props made all the difference in the world how this rig handles; especially when the slop shows up. And as the article you posted said..that can happen in just a matter of minutes. My rig would not run well, regularly bounced off the rev limiter. It would even spin the props and the motors would go into overheat alarm from cavitation when we were caught in 4-5 heavy chop one day last summer. Posted on several forums, and the 4 blade came recommended. Found a pair from iboats, and they replaced the stock Yamaha stainless 3 blades that were on my rig when I bought it. And I got the same results junior mentioned. Went from 15 to 17 pitch and 13 3/4 to 14 1/4 diameter. I am now well within my rated max rpm's..

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, going on the assumption that the rev limiter is not stopping the RPM at 6,400, but the motor is just running out of HP, then I will say that the

I am looking into a prop that has been recommended. 4-blade 14-5/8 x 16 Stainless

should work well for you, and lower the RPM to get it inside the manufacturers recommended RPM range.


H

 

[tmartin]

Re: Boat props x2 Help would be great!

T, going on the assumption that the rev limiter is not stopping the RPM at 6,400, but the motor is just running out of HP, then I will say that the should work well for you, and lower the RPM to get it inside the manufacturers recommended RPM range.


H

Thanks Hwsii. Your a great guy for providing all the info you do..

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, please come back and tell me how everything goes and if it is doing right.


H

 

[tmartin]

Re: Boat props x2 Help would be great!

Houston, I think we have a problem!

It was ugly. 14 5/8x16 SS 4 blade

I wanted to cry it was so bad. Those can't be the correct prop. I'm hoping by design..Not by size. It was ugly....

First of all, a definitely blew through the low end. Cavitation everywhere! If I full throttle, I'll blow right to the point Im on-plane. Which is like 1-1 1/2 boat lengths. Then it's the moon for RPM's. Over-rev kicks in and takes me down to like 5800. BUT, If I baby the boat on plane, I can get her right to 6000--perfect--speed is like 38mph... If I turn the wheel either way 1/3, the motor on the opposite side immediately cavitates, alot!

I believe my motors are too high OR the four-blade is grabbing more water than the hull can move forward to provide water to the prop...? Does that make sense?

I'm gonna try a 17" Honda prop 3-blade aluminum. I forgot I had one. So, tomorrow I'm gonna put the 15x17-3 on the starboard, and the 15.5x15x3 on the port. I want to see if the cavitation thing comes back...

I was beyond dissappointed...

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, going on the assumption that the rev limiter is not stopping the RPM at 6,400, but the motor is just running out of HP, then I will say that the

I am looking into a prop that has been recommended. 4-blade 14-5/8 x 16 Stainless

should work well for you, and lower the RPM to get it inside the manufacturers recommended RPM range.

T, I was right about the rev limiter, you are using way too low a pitch prop on the boat, and there is more speed left in it. Let me do some searching to see if I can find some more data.

Exactly what manufacturer and model of props did you get.



H

 

[tmartin]

Re: Boat props x2 Help would be great!

The props were Michigan Wheel Apollo XHS--I used the Honda Hub kit on each.

Interesting to note, I had soo much throttle left over I couldn't believe it. These motors want to take off!

I called the dealer and he told me the motors he hung (The BF150's) are the same length the Ficht's were that he replaced. So he really thinks the motors are the right height....frankly, I'm not convinced...I'm really worried.

My worst feeling is that once the boat was on plane, it lifted out of the water enough to cavitate. I have only one screw height I can lower and that would be the lowest setting.

Can the physical shape of the ears really make that much of a diff? Maybe a 17" 3 blade could work?

Howsii- Help!

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, the physical size and shape of the ears is what is called blade geometry, and that can make over twice the RPM difference than changing two inches of pitch. I have seen a 17" pitch SS prop go 5 MPH faster than a 18" SS pitch and turn over 1,000 more RPM, and both of them were manufactured by Yamaha. As well as the 16" pitch in the same model as the 18" went 5.5 MPH less than the 17" pitch and yet turned 700 RPM less than the 17", and we are talking about a maximum speed of 36.9 MPH with the 17" pitch, 31.5 MPH for the 16" and 32 MPH for the 18".

It requires knowledge of Prop geometry as well as hull forms to match the correct prop with the correct boat, as well as the intended uses of the boat by the owner and what particular problems he is trying to cure.

You might try and read this, it can be very boring if you don't understand blade geometry, but it gives you an idea of what can happen to people changing props, whether they change pitch or just go to a new model of prop, from the same manufacturer.

http://forums.iboats.com/showthread.php?t=303221

2. EXACTLY what manufacturer and MODEL of prop is recommended and who is recommending this prop, because I show you should be running a higher pitch prop than that.

Remember me asking this question, there was a reason I asked for it, maybe you understand better now.

All that excess throttle you have left over is partly because you have too small a pitch for the boat, and partly because the boat has less drag with the new SS props, because of the new attitude your boat is running at, and that is why you are getting bad ventilation in the turns and cavitation at startup.

Don't worry we will get you fixed up right.

H

 

[tmartin]

Re: Boat props x2 Help would be great!

Well, I think I'm getting closer...I tried something..

I ran my older Honda 225 prop. 15x17-3 blade aluminum prop. Boy did it do a helluva lot better than the 4-blade SS 14 5/8 x 16. Night and day difference!!!!

What I did was leave the CR-15" prop on the port and then put my 15x17 on the starboard. This is what I saw. On the 15 motor went right to 6400 or so. My 17 went to 5850. When I trimed my 17 up a bit, it barely hit 6000. Perfect! I saw no signs of cavitation either. Wow! What a difference a prop makes. Top speed was achieved with both motors trimmed up a tad, 15 throttle at 3/4 (leaving that 1/4 thgrottle that goes into rev limiter) and the other at full throttle and also 6000. Top speed was 40.8mph.



Newer prop 58130-ZY3-017A Honda prop says E3x15x17R

I think I found my prop-pitch. Now I want the best performance I can get.

Howsii-
SS 3-blade?

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, you might want to look at this, I found it while searhing on Yamahas site for a 4 stroke performance bulletin.

http://www.yamaha-motor.com/assets/products/otb/bulletins/bulletin_4stroke_hpv6_sws2_sa7c49.tmp.pdf


H

 

[tmartin]

Re: Boat props x2 Help would be great!

Thanks Man!

I hope to get out there this weekend....I still worry the motors are up too high...

The only "proof's in the pudding" line I can think of, is simply, If I can get-up on plane, and make some descent turns without blowing-out, THEN I will rest easy.

I did some calculations and If I can hit 42mph, my prop-slip may be like 6%-7%.

That's got to be alot better.

Now for the REAL question....how about the performance of that same prop pair (15x17) in Stainless....?

 

[housefull]

Re: Boat props x2 Help would be great!

I accept with information:I ran my older Honda 225 prop. 15x17-3 blade aluminum prop. Boy did it do a helluva lot better than the 4-blade SS 14 5/8 x 16. Night and day difference!!!!

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, I have NEVER waffled on reommending a prop for a boat like I have for yours. I think about it every day, but the variables involved keep me undeided.

I am going to list some of the things that are going through my mind:

1. The lift that you experienced with the Apollos is normally an excellent thing, because when you have more of the boat out of the water the faster the boat goes and the less drag you have. But with you only having one notch left that you can drop the motors, that is not good.

2. And then to add to that dilemma you also add an extra 1,500 pounds at times when you catch the fish, which is about 25% more weight than you normally carry, which requires more blade geometry.

3. You run your boat in very dangerous circumstances having to pass that bar with the river, tide and wind possibly creating circumstances that could either cause pitch poling or broaching.


In just want to think some more, I definitely have not forgotten about you.


H

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, I have asked Dhadley to help you with the choice of the best prop for your boat, as quite frankly I believe he can do a better job than I can in these circumstances. I do believe it is very important for you to have the BEST prop available because of the guidelines you use the boat under, and Dhadley is MUCH better than I am.


H

 

[Dhadley]

Re: Boat props x2 Help would be great!

Just going over this quickly a couple of things come to mind. When testing you always need to test with an average load. Testing with something other than an average load will skew the test one way or the other.

The 4 stroke motors should be set up to 6000 rpm - with your average load. The rev limiter probably is around 6300 or so. Some injected motors go "full rich" as the limiter, some motors scatter the spark. In most cases the limiter is so subtle you think it's running fine, just won't go any higher. In any case when we think we're aginst the limiter we throw on bigger props (more pitch) to verify the baseline.

Most 4 stroke motors won't have a lot of low end torque. However, if your top rpm is at 6000 or more then your holeshot should be as good as it gets (generaly speaking).

Motor height - the X dimension depends largely on what type technology is in your props. Rule of thumb as fas as set back goes - you can go up 1" for every 5" you go back. Then take in to consideration hull design, transom angle, toe in, prop direction of rotation etc. There is no exact number or height. Most dealers won't have much, if any, experience in this type set up. That's why they haven't been much help giving absolute numbers.

If I were doing this set up I'd start with checking the set up and then verifying the rpm and - if accurate - throw more pitch at it just to work on the top rpm / speed baseline.

 

[Dhadley]

Re: Boat props x2 Help would be great!

Not sure if I'm any better at this but we have delt with some multi-engine deals. Not a great deal different than a single but some. Nothing more than having been exposed to it before.

 

[hwsiii]

Re: Boat props x2 Help would be great!

I appreciate it Dhadley, as soon as he gets back he will get with you.


H

 

[hwsiii]

Re: Boat props x2 Help would be great!

T, where are you?


H

 

[tmartin]

Re: Boat props x2 Help would be great!

Sorry guys, my 4 month old daughter has been taking up all my time..

So, then a 27" setback of 5.4" means my 4.5" actual motor height above the hull is right in there.

Now, this weekend I hope to get the boat out. I promise I will let you both know the results..