Prop ideas for SR5.4 & yam 90? - Page 2

RIB-Teccie · 25 October 2013, 15:41

Agreed, unless you have a racing engine and wads of cash to rebuild.

C-NUMB · 25 October 2013, 16:32

Quote:

Originally Posted by RIB-Teccie

Agreed, unless you have a racing engine and wads of cash to rebuild.

Yes, think they squeezed 115+hp in offshore 3B but not for very long before rebuild....

RIB-Teccie · 26 October 2013, 18:16

I informed the yamaha over rev limiters kick in at 6200 RPM, this from a much older mind than mine, who used to work at Yamaha.

Kat1nka · 26 October 2013, 18:25

Quote:

Originally Posted by RIB-Teccie

I informed the yamaha over rev limiters kick in at 6200 RPM, this from a much older mind than mine, who used to work at Yamaha.

Thanks ! 6200 RPM is very high for a non-tuned engine. My friend used to run his "sport-racer" at 7000 RPM WOT

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RIB-Teccie · 26 October 2013, 18:29

The Rev limiter is primarily there for when the boat is airborne, to prevent damage upon re-entry. It's not something to prop to. At 7000 rpm, the limiter must have been disconnected.

Kat1nka · 26 October 2013, 19:34

Yes, no limiter, but that was not the only thing that was changed on the engine

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But racing engines are a whole different breed than my standard old 90...

I am just trying to find a good SS propeller that will reach at least 5500 RPM at WOT with me alone and not loosing the topspeed I have with the 21 alu. I find it hard to accept that an alu propeller is the best one for my Searider. So far I have tried 5 different SS propellers and next step is to lift the engine one or two holes to see if that improves things with the SS props. I have been told that 1 hole up could raise RPM by 200 ? But that depends on the hull.

After switching to an SS on my other boat I also raised the engine. The result of he switch was a little higher topspeed and a lot better grip in turns and rough sea. And that is what I am looking for my SR as well

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RIB-Teccie · 26 October 2013, 22:44

I'm looking at your earlier post.

RIB-Teccie · 26 October 2013, 22:57

You are getting 5700 With a 17 pitch. You are getting 5250 for sake of argument from a 21. I'm sure the answer would be a black stainless yamaha 19" prop. The alloy should be no different . Your SR is the 4.7 and I can't remember what HP they are rated to. The 5.4SR always went well one hole up, ie Cav plate one inch above bottom of boat (some on this forum disagree), this may be I was used to a 5.4 offshore oil (crewed with 4 and fuel). I think two holes up could starve the top cylinder of water, which would seize the top cylinder. I've always found the bushes in non-standard props to wear out prematurely, and because of this have little experience of non standard kit. Also note, if you google yamaha prop sizes and get on the yamaha site, you will see some of the props with the same pitch have different diameters as they are more suited to the deep vee hull. Make sure you get the right one. I think yamaha sell cupped props as well.

RIB-Teccie · 26 October 2013, 23:09

Just had a look for you. Alloy deep vee is 13.5 x 19, the black stainless is 13 x 19. The pro series is 13.5 x 19, matching the alloy deep vee, which arguably could be a better choice than the black one. I think you should settle on transom height first. The 17 is clearly a waste of time, so try it with the 21, once you drop to 19, the improvement should be clear.

Kat1nka · 27 October 2013, 18:52

Thanks for your answers RIB- Teccie.

So I raised the engine this morning one hole. It is now at the second highest setting.
Changed the prop to the Quicksilver Vengeance 13 x 18. Into the water and out testing. The tach showed 53-5400 rpm at WOT, speed 41 knots. Fast hole-shot, almost no chine-walk, good grip in turns. I gained 1/2 knot and 50-100 rpm by raising the engine (same prop, driven in similar conditions on monday)
Back to the harbour and on with the old 21 inch alu. WOT 53-5400 rpm, speed 42,5 - 43 knots with some chine-walk and loosing grip in turns if I dont trim in the enine in turns.
So the search for a perfect prop continues next spring as we are slowly prepearing for winter over here

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RIB-Teccie · 28 October 2013, 09:48

In a honesty, I'm wondering if the boat may be operating above its horsepower rating. I'm not sure what the recommended max is for the. 4.7, it may be the hull is just a touch short for the power. If there is no chine walking with the 18, that may be as much as you can do, other than gamble on a 19. But if the chinewalking begins at 19, you may have wasted your money. After all you are only losing a knot or two but gaining good handling with the 18, and as you have found out, propping is always trial and error.