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Am I propped right?

Unishot

Unishot

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Hello everyone.
I've been thinking that I may not have the right prop on my boat. I bought it used, and it does not have the original prop on it. Here are some details, and I am hopeful someone here can enlighten me if I should expect better performance:

The boat is 26' long, with twin 32" elliptical tubes. It is a heavy "R" model with dual captain's chairs at the bow, and two fishing chairs/live well at the stern, behind the changing room/sun pad. It also has a sink and wash-down, so I normally have the 15 gallon water tank for it full when out on the lake, along with a full 30 gallon + gas tank. We normally have two ice chests full as well, which further adds to the weight.

The engine is a 150 Yamaha V-Max (6 cylinder two-stroke) and the prop that is installed is a Mercury Vengeance 15 pitch (3-blade).

With just my wife and I on board, and the above items, along with the normally carried stuff like tackle boxes/life vests/fenders/anchor/ropes/etc. I can get 5600 RPMs at wide open throttle. This equates to 28-29 MPH via GPS. Should I expect to get more top speed? Is this the max for this big of a boat/motor combo? The toons aren't perfectly clean, but they aren't really dirty either. (They were spotless about 6 lake outings ago, and only now have a very slight roughness to them under the water line.....kind of like a fine sandpaper).

I've heard good things about the Enertia and Reliance props, but don't know if they will even fit on this 2009 model engine, or, if it would even be worth the expense if it would only result in a small (2-3) mph improvement. I have no idea what the original prop on this boat was...

Any and all information you could provide would be greatly appreciated.
 
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Do you have lifting strakes on the ellipticalls? I don’t what the top rpm is for that motor, but a 15 pitch isn’t really off that far. Find out the max rpm and see if it has strakes. Without strakes I think you’re looking at your top speed.
 
It has no strakes. I was thinking that the wide open throttle should be a bit higher, but of course, there needs to be some room for over-revving/etc.
 
That seems slow to me... Elliptical are the fastest hull, and that combination (150 HP with a 15p prop) is very common here. I have that setup myself.

Someone with that set up will chime in, or you can look through the power section and try to find one.

Did you notice any speed change from your initial runs with clean toons? My boat comes out after each use (toons stay clean), but people here say half speed is common with dirty toons. Not sure what that means exactly.
 
I trailer the boat, so it never stays in the water. The toons aren't really that dirty. I noticed no drop in speed since earlier in the year. I would've thought that the top speed would be higher myself, and I remain perplexed on what to do.
 
WOT on a 2-stroke I believe is different than a 4-stroke. Do you adjust the engine trim while you're out? I just looked it up and 4500-5500 WOT. You might try a 17p prop.
 
Yes, I do Try to trim it. The motor is on the lowest mounting on the transom, and trying to trim the motor up a little causes it to increase the RPMs. I cannot get it to 3/4 trim.
I thought I read somewhere that the engine had a WOT of 5500-5800. I figured since I was at 5600 it was okay....
 
I just checked the online owner's manual and it does in fact confirm what you stated. WOT should be 4500-5500. Admittedly, I'm pretty clueless about what happens when increasing pitch or diameter. Would going to a 17P prop lower the RPMs and increase speed?
 
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I was seeing the same rpm at wot that Unishot indicated above for your 150 VMax: 4500-5500. Thus, you are just past the high range for your rpm’s on that motor. You have a lot of room to bring down rpm’s, and in doing so maybe increasing speed.

I’ve been told you drop about 200 rpm for each one point increase in pitch size. That was true on our boat when I was dialing it in last year. I would minimally go up 1 pitch simply to get rpm into the Yamaha recommended range for the 150 VMax.

For some interactive online guidance, maybe go with the Mercury Prop Selector: https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

Yamaha has an online prop selector too, but I don’t like it as much. Maybe its just me, but I find the Mercury prop selector easier to use and fine tune by boat/hull/motor manufacturer, etc.

With the Mercury prop selector I was able to fine tune the specific motor (hp/type/year/gear case/etc), boat size/weight, intended use I went with all around performance, but you can customize that too...

The picture below are 7 ideas the Mercury prop selector indicated as possible starting points. Prop pitch range seems to be where you are at, so maybe prop type or prop diameter are playing into your rpm’s. I would be inclined to try one of these suggestions, but move up to a 16p or a 17p because of where your rpm’s are at.

1682A87E-ACDA-4EF2-A70D-F535C544C42A.png
 
I played around with that, and one of the props suggested is the Vengeance that I already have on the motor, in 15 pitch. How much speed increase should I expect if I go to a 16 pitch, and how will it affect pulling large tubes? In other words, what is the trade-off?

Some of these prop calculators state that I should have a top speed of about 38 mph! (such as the Mercury one above). If I have the exact prop listed on the chart (the Vengeance in 15 pitch) I don't see how the calculation can be that far off, unless they are not taking boat size/weight into consideration. The calculator would not let me enter boat weight/size along with performance goals. I had to choose one or the other, and it stated that performance was "more accurate". Color me confused again....
 
Sure seems like weight would be better factor than performance tab in your case just because you have a heavier R. Also, I find their expected perforance a bit off sometimes, and really pontoons are so different from one boat to another, I really think to get totally “dialed in” you gotta do it on your own boat. However, you should be able to have a safe ballpark.

Normally I’d think you should be up there where they say, but I don’t know the impact of not having lifting strakes on the elliptical tube set up. My ONLY experience is on tritoons, and over this past year, with our SPS Bennington Tritoon. Also, do you have underskinning? My thoughts are is there a lot of water drag perhaps if no underskinning, mixed with sitting lower and not getting up on plan without the lifting strakes. However, I simply don’t know if the elliptical should sit you up high enough for these things to not be a factor.

I hope others with elliptical can give you better advice and since of realistic expectations.
 
Thanks for your reply. No, I do not have underskinning. I'm still trying to find the answer to the question:
If I go up to a 16 pitch, and RPMs drop by 200 or so, how much will the top speed increase, if any? And what is the trade-off?
 
Not much would be my guess. Seems I recall reading about 2 to 3 MPH.
 
Hmmm. With 26' ellipticals and no lifting strakes to get them up on a step I would think that you're doing as good as can be expected, even more so perhaps. Remember, without those hard chines, the logs are fatter versions of the standard 25" tubes on so many other boats. Long displacement hulls if you will.

Lightly loaded with you and another person (and normal gear) your 100 RPM's to the high side of your normal operation range. Add a few more people and fun gear for the day and I'll bet that drops as the pontoons carry more load and lose whatever lifting ability that their 32" of fat diameter were able to provide.

Almost sounds like you're right where you need to be. Also, be careful. By paying attention to the top end you may hurt your mid range performance when the boat has more people onboard.
 
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