Aluminum to stainless opinion

[ttankmoran]

Hey guys I have a Warrior fiberglass V166 fishing boat (tiller) with a 97 yamaha 70 2stroke
I am currently running a Yamaha 17K Aluminum 13.25"x17, with GPS, trimmed out, I am seeing about 34.2 mph at 5600 RPM this is with a typical load in the boat, 2 guys (360 lbs) Vantage, two deep cells, tackle, etc.

RPM range 5000-6000
gear ratio 2.33

I usually run in deep clear lakes and don't have to worry about rocks or other underwater objects so I am interested in maybe seeing slightly better performance with a SS prop, I dont have any complaints right now, it still jumps up on plane pretty decent even with full live wells and 3 guys, but since I have 400 rpm more to work with while dealing with a typical load I think I can improve holeshot and pick up a little speed at the same time.

I can turn this engine up to 6000 rpm

With a typical stainless prop would you expect a 16 pitch to be about equal top rpm-wise with the 17P yamaha prop?

Would you drop right down 15P SS and try for the couple hundred extra rpm?

Any opinions on SS prop brands/models? For the unfamiliar this is a deeper V boat as well.

 

[steelespike]

Are you saying your 17 will turn 6000 now with a light load?
We could tell better about your setup with the numbers with a light load. Your loaded numbers are really good you have typical range of slip at 11%.
It is reasonable to assume a 16" ss prop will produce about the same rpm as the 17" al prop.
Decreasing pitch to gain speed is a tricky proposition If your makling 6000 now with a light load I would suggest a 17" ss prop if your looking for more speed.
If you were struggling to make rpm then a decrease in pitch may get more speed.
You might consider a Turning Point Hustler prop in a 16.It is an aggressive al prop said to produce ss performance.

 

[ttankmoran]

Thanks for the info/prop suggestions. To clarify, with a light load with just me and perfect conditions I will see about 5700 rpm and 35-35.5 mph

Another clarification, this engine should pull right up to 6000 rpm. It is a P60 with boyeson reeds, larger bore carbs (70hp size) and aftermarket exhaust, I just said 70 hp because that is the rpm parameters I need to stay within (5000-6000)

As another comparison when it was a stock 60. I would see about 32.2 MPH at 5300 RPM with two guys and about 33-33.5 mph at 5400 rpm with just me.

 

[Texasmark]

The Turning Point Hustler advertises to have all the amenities of SS props except the blades are thicker due to the material being aluminum but they advertise a tough blend of materials in their alum. producing a thinner, stronger blade than the average run of the mill. Most Hustlers include porting. I have one and 3 SS Ballistic props. It compares favorably.

First off, "You aren't going to get blood out of a turnip". There is only so much your engine can do for you. 11% slip that Spike calculated is hard to beat with your spending who knows how much in time and money on doodling with different designs to get it better on a conventional hull.

If you want to go faster with this engine you have to improve on something. The numbers are telling you that you are currently maxed out. You can't get more rpm and more speed without changing something...less drag (which weight is a factor, hull trim, hull shape, engine position, more hp.

Raising the engine has a profound effect on performance, even just an inch. BTDT However, doing that puts the prop closer to the surface and increases the chances for ventilation, especially at high trim angles in tight turns and in rough water conditions....assume you have power trim. A cupped prop, like a Hustler grabs better under these conditions, everything else (pitch, blade shape, rake, blade thickness) being the same....aka same series prop from same mfgr.

My reply is based on non professional education (self taught) and experience.

 

[Sea Rider]

The rule of thumb that states 150-200 + reves per pitch decrement will probably not work in your equation achieving more rpm than expected by this near formula.

It's very difficult to dial best prop performance in a single try, usually need 3, that's 2 inmediately after stock prop change. After testing first 16 SS prop will know max wot rpm achieved, if in need to be close to 6 K rpm drop one pitch to 15. I wouldn't drop pitch straight to 15 as you could blow by way far the rule of thumb specially on medium light boats with modified outboards.

If you aim for 6 K wot revs as usually loaded, expect engine to over rev with you alone, if engine doesn't have a rev limiter, watch your tach when speeding alone at wot. Less pitch will increment hole shot performance along nicely moving more weight once on plane, but will lose some top end speed.

Happy Boating

 

[Texasmark]

It's no big deal to raise the engine. Get a helper and a piece of 1x2 wood. The wood will go between the engine clamp bracket and the top of the transom to support the weight of the engine. Jack up the tongue of the trailer till the skeg is on the floor. Undo and remove the bolts. Continue to jack the tongue up until the next set of holes lines up. Replace and secure the bolts. Let the tongue down on your vehicle's trailer hitch. Go to the water and test. If you get your speed but have a little ventilation problem then get a cupped SS prop. We can talk about which one when you get back!

 

[Sea Rider]

If at plane on flat calm no wind water cond don't have water splashes over or out transom, can make tight close turns, don't need to raise engine, You're right at the sweet engine/transom height. Why do you need to fully trim down if it's a tiller driven combo. You should trim engine to be perpendicular at (90?) deg angle for anticav plate to ride parallel to sea level, provided that boats is well balanced with weight evenly distributed on deck.

Trim as suggested and check again at wot, probably your top speed will rise a bit. If with water splashes over transom will need to raise engine with shims accordingly untill water splashes disappears.

​Happy Boating

 

[Texasmark]

If at plane on flat calm no wind water cond don't have water splashes over or out transom, can make tight close turns, don't need to raise engine, You're right at the sweet engine/transom height. Why do you need to fully trim down if it's a tiller driven combo. You should trim engine to be perpendicular at (90?) deg angle for anticav plate to ride parallel to sea level, provided that boats is well balanced with weight evenly distributed on deck.

Trim as suggested and check again at wot, probably your top speed will rise a bit. If with water splashes over transom will need to raise engine with shims accordingly untill water splashes disappears.

​Happy Boating

Gotta be pretty deep to have water splashing inside....deep enough to submerge the deflector built into the front of the LU to prevent such. Never had an engine low enough to cause that. Height I'm talking about that deflector is a couple of inches or so above the water coming out from under the transom. If you never used engine height in your setup to improve performance, you might try it some time.