New Props - Too high?

[Paul_Dublin]

I tried some new props over the weekend.<br />Have Twin 60's on a 5.8m RIB.<br />Originally came with 15" - Could probably pull the titanic and would throw the passangers off the back when I gave it gas, but not top speed.<br />Changed to 17" and seemed a good change. Less acceleration and pulling, but about 5mph extra. One motor would still peak at about 5800 if I didn't back off. It would also plane on one motor.<br />Changed to 19" at the weekend, and the revs have dropped to a max of 4900 (unless I trim up quite a bit).<br />The speed is about another 5mph, but it seems like a big drop in revs for just 2".<br />It will struggle to plane on one motor now.<br /><br />The 15" and 17" were OEM Yamaha, and the 19" is a SOLUS.<br /><br />Is there any reason the revs would drop so much with only a 2" change?

 

[Ray Neudecker]

Re: New Props - Too high?

Many other factors such as diamater, rake ect get in the picture besides pitch when you change types or manufactors of props.

 

[Paul_Dublin]

Re: New Props - Too high?

Diameter went from 13.25 for the 17" to a 13" for the 19".<br />Didn't actually look into rake or any other factor.

 

[ThomWV]

Re: New Props - Too high?

Paul,<br /><br />This is a problem that Suzuki owners get used to but not so much with other brands. Its the way that the pitch is calculated by the manufacturer that seems to be the problem.<br /><br />Most props are not made like fan blades, with a straight ear welded to a hub and a constant pitch from the root to the tip. With most props the actual pitch is different along different segments of the blade. So when the manufacturer assigns a pitch to a particular model what they are doing is calculating a weighted average pitch taken from several data points along the leading edge of the blades. That means that a 17" pitch prop of some diameter with some rake from one manufacturer may not perform the same way as a prop from another manufacturer even though the same specifications are listed for both of them. That's because they may have used different weighting schemes in assigning a pitchs to their props.<br /><br />I mentioned Suzuki props up from as an example of this because they are best known for it. If you take a Suzuki prop that is indicated to have 20 inches of pitch it will likely have about the same performance characteristics as a prop by most other manufacturers with a 17 inch pitch. Suzuki props tend to be overstated in their pitch by about 3 inches compared to others. <br /><br />So I think that may be what you are seeing right now. I would take a guess and tell you that if you were to try out a 19" pitch prop by Yamaha it is going to give you the same sort of gradual performance changes you saw when going from the 15" to the 17" and will be quite different than the results you got out of the 19" Solus.<br /><br />Thom

 

[ivar]

Re: New Props - Too high?

In addition to what ThomWV says, the SOLAS prop can also have more cupping , giving the effect of a little more pitch. <br />Also, blade thickness and design will affect rpms, I have a 15' boat with a 60 Yamaha. With the 13x19 I got 5800-5900rpm , so I got a 12 5/8x21" michigan for it, it dropped my rpms down to 51-5200 with only a slight increase in speed.<br />It looked more crude than I was used to from the Yamaha props I got, so I sent it to a Prop doc for some massaging , and now I can run 5500 all day long, which is the recommended top rpm for the engine. <br /><br />BTW, Here in Norway , the Yamaha props have gone down a lot in price recently and now cost only slightly more than a Solas/Michigan, I think I'd look into getting the Solas returned and getting a Yamaha 13x19 instead.

 

[Paul_Dublin]

Re: New Props - Too high?

I really doubt the shop will take the Solus back after using them. And If they do, I'll be stuck using another Solus.<br />When you say massaging, what do they actually do?<br />And how much?<br /><br />Paid about 130Euro each for them, so not a huge amount, but they are not really doing what I want. Yam props are looking at about 200Euro each unless I get them imported from the US (about $100 each).

 

[ivar]

Re: New Props - Too high?

A "prop doc" can reduce/increase pitch , add more cupping, make the blades thinner, reshape edges etc. And just do a little TLC to make the prop work smoother, after I got my yamaha 13x19" in for repair , it was better than new..! <br /><br />The prop prices for the Solas sounds similar to what we pay here, the yamaha prices were 2-300? here too until last year.

 

[Spidybot]

Re: New Props - Too high?

Many seem to be happy with Hustler, available from this site (link on bottom). Good value and nice hub-system if you want to switch props at some point.<br /><br />If my memory serves me, there was a fella in UK offering these props.