Same pitch and diameter, lost 1000rpms

[Wwohl]

Hello iboats community.
I recently purchased a solas Rubex prop to replace the factory one on our Yamaha that was damaged.
The boat is a 23 ft pontoon with a 115 Yamaha. The factory prop was a 13.25x17K (3 blade). Typically ran 24 mph at WOT at 5500 RPMs.
I purchased a 13.3 diameter 17 pitch 3 blade Rubex prop from iboats in aluminum. After install, my WOT with an empty load was 4500 RPMs and still doing 24 mph.

I thought I was buying a direct replacement. Any help?

Bill

 

[steelespike]

Is the motor a 4 stroke? It definitely appears that a 17" is out of place whether a 2 stroke or 4 stroke.
The 17 is too much prop ,gear ratio 4 stroke is 2.15, 2 stroke is 2.00 .2.15 is easier to turn the prop
4 stroke tests generally run 13" props with 15 used to a lesser degree.
I would guess the 17 had been re pitched or damaged.
test rpm was close to or at 6000 speeds ranged 24 to 34 with 2 log toons. Again the tests were 4 stroke with a 6000 max rating.
A 2 stroke has a 4500 - 5500.rating It does appear that a 15 would put you at about 4900. a 13 at about 5300.
​ Keeping in mind the rule of thumb 150 to 200 rpm per inch of change.
At 4500 and 24mph your at 33% slip, at 5500 you were at about 45%, bad.
Increasing the prop rpm should improve slip and could result in a little more speed.

 

[Sea Rider]

With that prop you're running into the lugging zone which is bad for the engine, specially if those wot numbers were obtained while solo boating lightly loaded. The scenario will be much worse when havining more load or passengers on toon.

Why don't you return to original Yammie prop assuming it was the original delivered one, you already know what to expect, instead trying different ones which is a costly option to match same previous performance.

Could even drop one pitch less to pull your wot revs up near 6 k revs if that number is or is near the max wot rpm factory stated for that engine, will achieve better hole shot and be able to move more weight better,

Happy Boating

 

[Wwohl]

Yes it's a 4 stroke on a 23 foot pontoon. The previous Yamaha prop was the original. The boat is only a season old.
Obviously I'm going to have to go back to the much more expensive Yamaha prop. I'm just really surprised there was that much of a difference with this new prop. Obviously one of these two isn't true to its dimensions and specifications.

Unfortunately the prop can't be return since its been in the water. I'll be contacting iboats and solas Monday morning to see what they have to say

 

[steelespike]

First of all the Solas 17 is working really well 33% slip it's just the wrong pitch.The Yammy 17 for what ever reason is at 45% slip just plain awful.
If the Solas was the right pitch 13 or 15. the rpm would be higher and the slip even better.
I'm pretty sure I read somewhere that Solas makes props for Yamaha.
At least check all the pontoon tests in the Yamaha Performance Bulletins note those with 2 tubes.
You don't need a different brand just the right pitch.

 

[Tail_Gunner]

You probably need to setup the pontoon right from here it reads a bit under the weather. First would be to raise your outdrive until that 17p starts slipping when cornering or when your running a heavy load..or clean the tubes there full of growth and pulling down your toon badly. That new prop is hooking up nicely that's all that is going on here.

 

[Wwohl]

First, thank you for the replies. I agree, it seems the yamaha prop was at 40% is slip which is very high. The current prop seems to be performing much better, I'm still just surprised how much so.
I spoke with iboats this morning and sent an email to solas. Hoping to hear back from them soon. It looks like I'm going to need to buy another prop and sell this one. Really sucks that I can't return it.

Now the trouble is, Ive gotta select another propeller. The 17 pitch prop is currently only allowing the motor to turn 4500-4600 RPMs at WOT. So I've gotta drop to a lower pitch. Im not convinced that the 15 inch pitch is going to give me enough change in RPMs. Looks like Im going all the way down to a 13 inch pitch.
Im worried that a 13 inch pitch is going to drastically reduce my top speed. However, assuming that the slip is low like this current prop, I guess not once its operating back in ideal RPM range.

Any insight from here. I was trying to help my old man out by picking him up a new prop for the boat that was a direct replacement and now all of the sudden we are $85 in the hole because we can't return this prop.

 

[Sea Rider]

It's very difficult to dial best prop for a given application after testing original delivered prop as you will not know if going one less pitch if revs will lessen 150-200 rpm as per rule of thumb, a pity that you can't test spare props to dial best one for your current toon application. BTW, is it possible to plane that toon while lightly loaded or just achieve fast displacement non planing performance ? How many passengers will that toon carry most of the time ? You will need to dial a prop that achieves at least middle to max wot numbers for engine to work relaxed while loaded at wot.

Won't be able to dial best prop to achieve best top speed and best hole shot, usually is best hole shot with less top speed or viceverse, one cond opposes the other. On a toon is better to have best hole shot with slight less top speed, toons have more hull drag to overcome fast compared to hard hull boats.

In my particular case wanted a prop maximization, went from original prop to one less pitch which was supposed to put me in the safe max wot rpm, but achieved 600 + revs compared to the factory delivered prop, so will order a 0.5 less pitch prop to be at the sweet max rpm range for my engine. Best scenario for you will be ending buying a third prop if second one doesn't dial running engine inside middle to wot rpm range.

Happy Boating

 

[steelespike]

Keeping in mind your origina17"? prop has 45% slip And your new 17 is at 33% at the relatively low rpm and increasing the rpm should improve slip.
To get to 5500 you need about 1000. A 13" based on the performance bulletins really isn't too much of a gamble.
As you add weight the 13" rpm will hold up better than a 15".And it will have farther to go to drop out of the lower rpm range.
If you check the Performance bulletins you will see the speeds and and rpm with a 13" prop, for all intents and purposes rpm is 5900.
Your boat will compare to the slower ones.
As far as selling the 17 If you check the Bulletins I think you will see that the 17" is pretty common on normal
slightly heavier hulls like the popular deck boats.

 

[Wwohl]

Here's what I got from Solas,
"
First thank you for choosing Solas.

The original Yamaha K series props' blade area is smaller and the design is completely different from Solas YD series props. Therefore, even same dia x pitch might perform very differently. Everyt propeller manufacturer has its own design and thus which prop your boat likes the best might still need a real try."

Okay so I'm gonna need to order another prop. I'm worried that dropping to 13" will be too much of a change and 15" not enough. I could go with a 4 blade 13" but that adds another unknown factor.
Also, I think the 3 blade 13" is 13.75" diameter not 13.25 if that matters.
Any recommendations? And I guess I'm stuck selling the 17" on eBay?

 

[airshot]

This is a classic example of why it pays to deal with a local marina/propeller shop. They could have helped you in the beginning with your prop selection and if it were incorrect most all reputable shops would exchange there prop for another as long as there is no damage. Paying a little more to support local dealers can actually save you in the long run...it has for me many times.

 

[Sea Rider]

Buying new props to test could result in huge waste of money as this is not a exact rocket science. Props must be tested onder trial and error and may need many to dial best one for current application. Better stick with what Airshot recommends : Go to a local marina/propeller shop and ask for HELP.

Happy Boating

 

[inthedirtagain]

Well, I don't have any advice to offer, but I can tell you I'm in the exact same "boat." I just dropped $183 on a new prop and hub for my old Merc ToP and lost about 800-ish rpm. I also contacted my local boat shop, whom I do all of my business through, and he wouldn't take it back once it was in the water. His advice was to try to verify the accuracy of my tach before buying another (potentially wasted) prop.

I was running an old 17p prop that was a little tweaked and could hit 5200 with just me, and about 4900-5000 w/6 of us in the boat. In my little 16ft closed-bow, that should have been pretty close to the right prop (69 Silverline, Merc 1000). I wanted to pick up a few rpm, so the shop sold me a Black Max of the same diameter and in a 16p. I didn't have my GPS or phone with me, so I couldn't verify my speed at WOT, but judging by the tach, I'm not so sure what to think. I could only hit 4400 with just me and my 13yo son. I'm going to buy a little inductive tach to verify my rpms when I do another WOT run. You may want to try the same.

 

[Wwohl]

I spoke to four local marine shops. Most of them only sell factory replacements and none of them have spares for me to test for my application. Also have a no return policy. ****

 

[Sea Rider]

Gee very bad music, what do you plan doing ?

Happy Boating

 

[steelespike]

I don't understand the mystery. If you check all the Yamaha performance bulletins for 2 tube pontoons.
You'll find that 15" and 13" are common for a 4 stroke 115.I think leaning more to 13 than 15.
It's very true it could end up being a 15 but you can still use the 13 by watching the tach.
If you go 15 and its too much you simply can't use it for an extended time.
Check the bulletins ,2 tube pontoons note the pitch,rpm and speed then tell us what you think.
As with all pontoons they are unpredictable a little more than a mono hull but thats the gamble of prop selection.
At least if you sell the new 17 you will appeal to more than just a pontoon.

 

[Wwohl]

Yea just gotta figure out where I'm gonna sell it. Guess ill post on eBay..

Confirmed today. 25mph and 4500 RPMs at WOT with two people on the boat. At 100-200 RPMs per inch of pitch, I'm definitely going to need at least the 13". I can't imagine needing lower than that. Switching to an 11 would be such a huge change from where I started. Hopefully the 13 magically gets me into the desired RPM range.

 

[Sea Rider]

Are 100-200 + RPM per pitch achieved while wot testing or going for rule of thumb ?

Happy Boating

 

[inthedirtagain]

Im still in the same "boat." I ordered a Tiny Tach so that I can verify rpm and see if maybe my stock tach is losing accuracy. In addition, I also verified that I was truly getting full throttle at the 3 carbs when the throttle arm was all the way forward. I may not have previously been getting a true full-throttle condition. I am now, but I'll probably be selling the 17p prop on ebay, too.

 

[Wwohl]

Hello boats community,

I wanted to give an update for future readers... I spoke with iboats customer service who was great.. However we still aren't quite perfect.

As you recall, the original 13x17 prop was 24 mph and 5500 RPMs at WOT.
The replacement SOLAS Rubex 13x17 was 24 mph at 4500 RPMs at WOT. (only one person)

So iboats customer service and i decided the next best option was likely a prop with 13" of pitch to get us into the ideal operating range. Going by the 100-200 RPMs per inch of pitch rule, we settle on the 13.

Well I got the 13x13 prop installed yesterday. Same SOLAS Rubex 3 blade as the 17 inch was. At WOT, we are at 22 mph and 6200 RPMs. WTF. And that was with 4 people, 3 dogs and coolers on the boat.

4 inches of pitch equated to 1700 RPMs for my application.

Fortunately, it seems the 15 inch pitch version will work well.