Yamaha F70 Prop Recommendation

[Lumpo414]

Im picking up a 2009 Alumacraft Classic 165 with a 2017 Yamaha 70 Four stroke. Boat is 16'5" with 82" beam. Looking for the best performance i can get out of this setup. Which hole do i want to set the motor height to? Any recommendations on a good performance prop? Getting on plane is more important to me than an extra MPH. Is anyone reflashing these motors to up the HP? Thanks for any info.

[99yam40]

what is the max HP the boat rated far?
what prop does it have on it right now?
and how does it run for you?

I would find a Yamaha Performance Bulletin for that boat and motor or something close, to see what prop they ran

[Lumpo414]

Rated for 75 it's a new boat to me so I haven't ran it yet. Im picking it up Monday but i know it has the original white aluminum prop that it comes with. Was hoping for some members with real world experiences and know of a proven prop to still reach max rpm of 6300 and gain some performance. I am definitely switching to Stainless Steel prop.

[99yam40]

Some like 4 blade props ,some do not.
does this have a pocket or tunnel and jack plate?

see what prop you have and how it performs before worrying too much about other props
I would still look up the performance bulletins

that is a wide boat, do it should come up quickly

[Jason2tpa]

You won’t know which bracket hole to use until you hang the motor....rule of thumb is ventilation plate 1” - 2” above/below bottom of transom. Start with the bracket hole that gets you in that inch range. You won’t know if a different pitch prop is needed until you water test the prop already installed....you’ll need rpm gauge of course. Target is top end of spec rpm range at WOT.

[Keithbaja]

With that set up (boat & Motor) you can expect very little gain with a SS prop. If any at all. The X spot (prop height) is very important. BUT,, just as in prop pitch. You must experiment with it. Or find someone with the same boat, motor, prop
Not likely. Propping a boat to the sweat spot is akin to triming a boat.. you can't make a vid or book
It's a skill that comes with many years of doing it. That said. You should always run with your avavege load. Your target is to hit WOT as the manufacturer recommends. I recommend to shoot for the high side of rated WOT. Also 1 inch of pitch is around 200 rpm gain or lose. Let's not start talking about RAKE, CUPING, number of blades. Do stay away from plastic blades. (U think) there is many down sides to a SS prop. I always recommend to new boat/Motor comble. Start with 3 blade alumanan. Most start with a 17p or 19p. Do not throw on a high pitch prop thinking you will faster.. nope ! You go slower and also dogging the pwr head. BTW if you want to go fast,, start with a faster hull and motor

[Lumpo414]

Picking up the boat sometime next week to test everything out. Thanks for all the input.

[Lumpo414]

Anyone know what RPM I will make max HP? Is it okay to run long periods of time at max hp rpm?

[99yam40]

I am sure an owners manual and a service manual would have the RPM
my guess is 6000 as max RPM.

I run chainsaws at top RPM all the time , but not for hours
I would not run a car or truck at top RPM for long either, mainly because I want it to last as long as possible

[Lumpo414]

Took the boat out for first time and one thing I noticed is under power it will only let me trim so far then won't go any further. All my other boats I can trim the motor out of water if i wanted under load. Is this normal?

[99yam40]

maybe you motor is set to low and the trim rams run out of range

[Lumpo414]

Current prop is 13 5/8 x 14 aluminum prop and at WOT and motor trimmed up all the way I reach 6300-6400 rpm according to my tach and get to 32.5 MPH on GPS. What do you guys think?

[TownsendsFJR1300]

RPMs are a bit high for my liking

Did you find an owners manual and get the spec's for the engine?

A quick search on-line:
https://www.rubexprops.com/boat-prop...e/?make=Yamaha

.

[pstephens46]

6300 6400? Good God man. When does the rev limiter kick in?

[99yam40]

4 stokes are higher rpm than the 2 stoke Yamaha motors

right now my C40 can hit close to 6K , but I will not let it
I think it will limit it to 6200


if his F70 is rated at 6200 the rev limiter should not kick in until a lot higher