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We're just finishing up our first season with a 1982 17' Montauk, which came with a Yamaha F70 mounted one-hole-up and a (presumably Yamaha Performance) aluminum prop, 13 1/4 x 17-K. Not surprisingly, RPMs top out around 4500 at WOT. I'm having the engine remounted three-holes-up in the off season, and would like to get a recommendation on a stainless-steel prop currently available that will get the F70 to over 6000 RPM with this configuration.

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It is not a Yamaha Performance prop since that one is polished stainless steel.

With a WOT of 4500, something is horribly wrong.

Is the hull waterlogged?

What is your load, passengers, fuel, gear? Bottom paint? T-Top?

Mounted 2 or 3 holes uo you can choose between these Whaler owner tested props. Keep in mind the blade designs are all different so that is why there are different sizes.

13x17 Yamaha painted stainless steel
13.25 x 14 Yamaha Performance Series
13x16 Powertech SCD

Note the WOT RPM's is 6300 so hitting 6k at WOT would be ideal. Anticipate 36-39 mph.

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Ouch - hope you (and the previous owner) did not damage the motor lugging it like that. Assuming it's OK, I can personally vouch for Phil's 3rd option, the Power Tech SCD3 in 13x16. I run one one my F70 on a 15, and it works great but is also significantly underpropped on my smaller boat - I hit the rev limiter (6450 RPM) when running flat out and light. I would think the 16 would work perfectly on a Montauk.

From my experiments the F70 runs best with a low rake prop with small blade area - the SCD3 was the 4th prop I tried and it was dramatically better than all the others. I went all the way down to a 13 pitch in a prop with more blade area and it still didn't have the acceleration of the SCD3 in 16 pitch.

I have been thinking of going to a 17 or 18 pitch, so if you are potentially interested in buying my 16, let me know. I see you are located in Massachusetts, as am I, so I would be happy to let you try before you buy.

Tim

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Tim - The 3rd listing is there as a direct result of your diligent testing.

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I have a 1970 Katama 17 with new F 70 , running a stainless 13.25 x 14 SCP Powertech prop . Absolutely perfect for my needs . Motor mounted 3 holes up . Runs about 6100 rpms at wot . Tracks straight as an arrow thru all rpm ranges . Prop was under $400 incl shipping from Dansdiscountprops.com .

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Phil T is right that something is wrong, but I think it's just the prop pitch and the engine height. The former owner seemed to have little interest in boat performance, and may have gotten a deal on whatever propeller his dealer happened to have in the shop when he reengined.

The bottom is a mess and will be sandblasted this fall, there is no top, we had two people on board and maybe ten gallons of fuel. This is really just a beach launch for us. I'm just trying to get more efficient operation - it's my wife's boat, I never drive it, and she never runs at WOT.

I'm going to buy and try Tim's 13 x 16 Powertec SCD, hopefully next week. It should help a lot, and once I get the engine raised, I'm sure I'll be happy.

Thank you all very much for your help, this is a great place to come for help!

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So this is the follow-up on the posting below. We put the engine to three holes up over the winter, and put on the 13 x 16 Powertec SCD prop. With two on board, WOT is 5400 rpm, and (GPS) speed is 30 mph. This is a marked improvement and we're going to leave it the way it is.

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Ocean - I still think something is wrong.

The wide open throttle range on the F70 is 6300 rpm.

I would expect you to get to at least 6K with that prop and hit 35-39 mph.

Running heavy and not using engine trim may explain your report.

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Crew and fuel would be about 400 lbs. Say more about engine trim...

Thanks!

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Phil's referring to trimming out the engine after hopping up on plane.

At displacement speeds, the engine is trimmed down all the way. But after accelerating and transitioning to plane, the engine needs to be progressively trimmed out/up as speed increases. This improves the propeller's angle of attack and reduces drag (and steering effort), resulting in higher engine rpm and boat speed.

If you are not trimming out the engine, you are leaving a lot of performance on the table. You are also likely exerting a great deal of effort to steer the boat while on plane.

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Sorry you're not getting better performance with the new prop, but every boat is different. To make sure you have a good baseline, take the boat out on flat water with a minimum load (just you) and do a top speed run - full throttle and then trim up to where you feel the boat performs best. The SCD-3 is a stern-lifting prop, not designed to lift the bow much, so you won't want to trim up radically as it won't help. Just trim up a little until you get what seems to be top speed. You should feel the boat really start to accelerate as you start to trim up.

I'm hoping you get up to around 6000 RPM and 35 MPH at least. If you don't, you may want to consider dropping down some more in pitch, but get that baseline first. I see the poster above ended up with a 14-pitch.

I'll be happy to buy that 16-pitch back - I have not had too much chance to experiment with the 17 that replaced it, but there were a lot of things I liked about the 16 so I'd be glad to have it as a spare.

Tim

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To much pitch, for sure-