20SC w/ 115 #'s and opinions needed

[Yz2009]

Ive got a 87' 20SF with a yamaha F115. Currently im running a 17p stainless yamaha prop. My WOT is 33mph at 5600rpm. Ive got a 4s so im propping closer to 6000rpm but i talked to ken at prop gods and he recommended the powertech RED3 (13 1/4X15p)

Heres the thread i started:
http://www.propgods.com/forum/defaul...g=posts&t=1707

[eggsuckindog]

Ken is very good at propping boats, he has done alot of them. There are so many different prop designs that behave so differently in different applications - he was probably right

[Yz2009]

keep in mind though ive got a 4s and youve got a 2s. Im propping near 6000rpm and you near 5500rpm. You may need a completely different prop but that thread should be a starting place.

Also my motor has a 2.15 gear ratio and im pretty sure yours has a 2 gear ratio

[mrobertson]

Before i spend too much $$$$$ i'm going to raise the motor a hole............unfortunately i only have 1 left to go before i'd have to re-drill. I will re-post this weekend with the results.

-Mike

[McGillicuddy]

Mike
The 15pnew black diamond might be all you need. You will find the holeshot impressive.

Yz, the RED3 is not the answer, I tried it. you would be better served by the pt props MQF3 as it offers much to more stern lift. Bigger blades and diameter will get more from your gear set.

[FishStretcher]

Originally Posted by Yz2009

Ive got a 87' 20SF with a yamaha F115. Currently im running a 17p stainless yamaha prop. My WOT is 33mph at 5600rpm. Ive got a 4s so im propping closer to 6000rpm but i talked to ken at prop gods and he recommended the powertech RED3 (13 1/4X15p)

Heres the thread i started:
http://www.propgods.com/forum/defaul...g=posts&t=1707

I run that same speed- 33MPH on GPS and engine speed- 5500-5600 with a Yamaha F100 four stroke on a 20 foot master angler. I have a 1:2.31 lower unit ratio and a a 4 blade 12 3/4 x 17 aluminum prop. Other than a 60 lb kicker and two console mounted batteries, the boat is pretty light and well balanced- a 20 gallon fuel tank inside the console, no T-Top, no leaning post.

Looks like you have a 1:2.15 ratio lower unit, so you should be a little faster at the same RPM and prop pitch.

I just raised my motor 1 hole to get the anti ventilation plate above the keel. I won't have results until next weekend.

It seems like you have a lot of slip? Unless you actually have a 15" pitch prop, or the 16" stainless prop that Yamaha makes. Which I want.

I'll post my findings in a week or so if that helps.

[mrobertson]

Step #1 -

I raised the engine to the last hole yesterday. A straight end from the bottom and a quick measurement and my cavitation plate is just slightly over 1" up from the bottom of the hull, i think around 1 1/4" higher than the bottom.

I put her in the drink to give it a test.

WOT is now 5100 RPM's @ 33 mph lightly loaded.

Going with a following sea i was running 27 mph at 4000 RPM and kicked it to 4200 - 4300 was giving me 29 - 30 mph. Pretty damn good cruise speed for a 115 if you ask me!!!

I am going to try a black diamond 15p prop soon and i will report my findings

[mrobertson]

Alright guys -

I've got my engine height where it needs to be. On plane my anti-cavitation plate is completely out of the water.

5500 RPM = Safe Operating Range

Black Diamond 13 3/4 x 17 aluminum prop gives me a WOT 5100 - 5200 at about 33 mph.

Black Diamond 13 1/4 x 15 aluminum prop.................i can peg that 5500 with more to spare with a full tank of fuel and 2 large adults. I'm not sure exactly how far above 5500 it would go, i was scared to let it wind up and damage the engine.

In any case - there's nothing that quicksilver offers that's between those sizes. I'm wondering if i go stainless on a 13 1/4 x 15 if that would be the ticket.

Holding it at 5500 (not going above) i was getting slighly over 35 mph trimmed out with the 15p.


Any thoughts????

[McGillicuddy]

Mike,

I think you have the numbers turned around. The 15p is likely 13-3/4 diameter and vice versa. Otherwise, sounds like you're there.

My guess is that the holeshot is greatly improved as is overall performance including fuel economy.

If you do go stainless the PowerTech 3 blade MQF15 is the ticket. It's also 13-3/4" diameter. Might gain a bit more speed maybe 2 mph and 5 to 10% fuel economy.

Good job and thanks for following up. Hope the rest of these guys were paying attention.

McG

[eggsuckindog]

Sounds like the 15 works better on performance at least. Different prop designs spin differently, a Merc Vengence would probably be about the same as the Alum BD for example. My suggestion would be a 15 Stilletto, it made about 300 RPM difference at the same pitch as my old one which sounds like it would be damn near perfect. The design on the prop works very well on the hull as I can attest. Their also a bunch cheaper than a Mirage + for example, I doubt you'll find too much used but I saw them new for under 300 on the net. Just MHO