Prop performance

[Pat K]

I recently switched from a 14 1/4" X 18 4 blade Quicksilver aluminum prop to a Solas prop of the same size and pitch. The boat is a Stratos 386XF with an F150 Yamaha. My top end went from 48 mph at 5900 rpm to 41 mph at 5100 rpm.

How can the same size prop from different manufacturers perform so differently?

[delcecchi]

That is very strange. You are getting the identical performance, since if the motor pulled to 5900 you would be going 48 mph. Something happened to the motor. Could be coincidence. Did you do anything else? Looks almost like you lost one cylinder.

[BoxMN]

Props can be that different. That is why you need to test lots of them before finding the one that is best for your wants and your boat. I would also say that Merc has a very solid and long tradition of designing, testing, and building props of all kinds, and they are pretty good at it, as well as having lots of different options even within the same size range.

Good luck, but it looks like you need to keep looking.

[JohnMickish]

I am going to say that the Solas prop just has to much cup in the blade for that motor on that hull. As menioned above, props can be that different even with the same specs. Take a look at some of the prop manafacturers info and you will see that many of them make a dozon or so props that spec out the same but have different attitudes in what they do. Think of it this way, a pontoon, bass boat, walleye boat and pleasure boat all have very different hulls, and with the same motor they need different props.

[Pat K]

delcecchi, you're scarring me talking like that. I thought of that but was trying to steer the problem in a less expensive direction.

I should check the compression first then look at the prop. Hopefully just need to go back to the Merc prop!

[delcecchi]

Going back to the merc prop would be an easy test. I just see no reason why there would be such a difference between props of the same pitch.

In the days when Bass and Walleye boats mag was around they used to do prop tests on occasion and they were pretty close in performance. Maybe a mph or two or a couple seconds on the hole shot.

How hard is it to take a look at the plugs?

[BoxMN]

Del, they never tested any alum props that I can recall though, at least not on anything larger than about 115 with alum, as most 115/135 and up really shine with SS as compared to any alum prop. B&WB Testing an alum prop on a 150 would be like Car & Truck mag testing a F250 with passenger tires

good idea on quick test with old prop though, unless it was dinged and thus the reason for the switch. Which begs the question, why the switch to the same pitch and size in alum prop? Our 150 is 2S, but I would think any swap would/should be to a SS on a 150 hp 2S or 4S, IMHO of course

[JohnMickish]

I just thought of this. If the new Solas prop is stainless you should have dropped your pitch one size. Since stainless flexes much less a drop in size is needed to keep your RPMs where they need to be.

[Pat K]

They are both aluminum.

The Merc prop got dinged up in Ontario is the reason for the swap.

We liked the way the boat performed with that prop, but a friend offered me a good deal on the Solas prop. I thought being the same size & pitch they would perform close to the same.

[delcecchi]

They are both aluminum.

The Merc prop got dinged up in Ontario is the reason for the swap.

We liked the way the boat performed with that prop, but a friend offered me a good deal on the Solas prop. I thought being the same size & pitch they would perform close to the same.

So the boat was running good in Ontario. You dinged the prop and came home, put on the new prop and now it isn't working right with the new prop. Is that the chronology? How bad was the prop dinged that you just didn't get it fixed?

I am still leaning on that it isn't the prop. Too big of an effect.

Could you have gotten some bad gas? Clogged up an injector?

[delcecchi]

Amazingly, bass and walleye boats HSOforum is still online, like a time capsule.

I couldn't find any prop comparisons but here is their quote on the stainless vrs aluminum.

Q: Are stainless steel propellers really faster than aluminum props?

A: Not really. If you switch from an aluminum prop to a stainless wheel (of the same style and pitch), you probably won’t see a big change in the boat’s performance.

But there’s more to it than that. Although aluminum is light, inexpensive, and relatively easy to repair, it isn’t a very strong material, so the blades on an aluminum propeller are usually fairly thick. Most aluminum propellers are good for general-purpose applications where price (or reparability) are the primary considerations.

Stainless steel, on the other hand, is about five times stronger than aluminum. Stainless props can be made with thinner blades (and in a wider variety of blade shapes and styles) than is possible with aluminum. Thinner blades and advanced blade geometries equate to better performance and speed. On a fast hull with a very positive power-to-weight ratio, stainless props can be faster than aluminum.

[Pat K]

There were quarter size chunks out of 2 blades.

There was about 3 weeks between hitting something with the old prop and installing the new one. It ran fine for a few trips with the dinged up prop.

I'll be doing a compression test tonight.

[delcecchi]

Well, so much for the bad gas idea. I still lean towards injector or ignition. But it could be something that would show up in a compression test.

It will be interesting to hear what it finally turns out to be. It is a funny coincidence it happened at the same time as switching the prop.

[Pat K]

Did a compression check, all 4 cylinders between 235 to 240 lbs.

Put the 3 blade 19" pitch prop that came with the boat on it and took it out on the lake.

Turned 5800rpm and 49mph on the gps.

Looking closer at the Solas prop when it was off the motor 1 of the blades looked like it was bent a little forward on the trailing edge. I set it on the garage floor and measured from the floor to farthest point from the center of the prop. The 1 blade was 3/8ths of an inch closer to the floor than the others. I hit it a few times with a rubber mallet to get it in line with the other blades. Ran out of daylight before I could test that prop. It will be my spare when the Quicksilver comes back from the shop.

The 3 blade prop has a better top end but the hole shot is terrible and the boat leans to the port side when I use it.

[delcecchi]

Ah, the Solas was bent. Did the "friend" who gave you a "good deal" know that it was bent? Had he ever used it?

I hate it when that happens.

[aanderud]

My goodness, I would have never thought that a slight bend like that could cause you to lose 15% of your speed and RPMs. Crazy.

[Kyhl]

That is unfortunate.

Sadly, eyeballing it back may not get it right because there are multiple angles at play. It may need adjustments to pitch, rake, and cupping.

[boatfixer]

Did a compression check, all 4 cylinders between 235 to 240 lbs.

I'm assuming you meant 135-140?

Glad to see you figured out the problem!