Correct Prop on New Boat?

[Kuusisto]

Hi All,
I've read up on props a little bit, but am still a bit confused about the relationship between pitch/RPM/speed.

I think the ideal wide open RPM for our motor (115HP Mercury) is 5500-6000 RPM. During our first ride with just the two of us and not much of anything else on the boat yet, we didn't crack 5000, I think it maxed out at about 4900 RPM at 25.x MPH. We will normally have at least a couple more people and more weight in equipment, coolers, etc. on the boat.

I've read it's not only less than ideal, but can actually be harmful if the motor is maxing out lower than the recommended RPM. We will occasionally tube/ski with it, but mostly just socially use the boat. Point being, my concern is that it is propped in the best way for the motor, not maxing out speed.

The boat was delivered new on Tuesday, should I contact the dealer and tell them I don't think the prop is correct? I certainly don't want to just be buying props trying to find one that is best. I'm not sure what prop is on the boat now, but can check when I'm home.

[Bryden24shp]

You are definitely way over propped. I would contact the dealer and tell him what's going on. He should give you another prop to try. He may suggest waiting until he break in period is over, but you'll want to break it in with the proper prop. I would drop 4" of pitch to start with, should get you close.

[Bamaman]

I agree with Bryan. It's hard to tell anything until you get a few hours on your boat when the engine loosens up.

And it should be up to the dealer to equip your boat with the proper propeller for the way you use your boat.

[RcgTexas]

I had way too much prop when they installed my motor. (their suggestion)

I bought an aluminum and started working on it. (cutting pitch) and a little diameter. When I like the results I will buy a stainless wheel like I want ...................or not. The aluminum is doing fine, and is sacrificial.

I think you will want those rpm to be about 5700 to 6000 when running wot. Then when you get a load your engine wont be loaded.

[kipper]

I had almost the same thing happen to me and interestingly enough it looks like we have similar boats. We took delivery of our Cypress Cay 230 Seabreeze with a 115 Merc Command thrust on it. With four people and about 15 gal of fuel we ran through our break in period and could only achieve 5000 rpm @ WOT and checked the speed via GPS at 22 to 23 mph. It would shoot out of the hole very strong but between 3/4 and full WOT there was no increase in speed and it only seemed like the engine was just making more noise and the motor did not feel like it was pulling. I ran the part number off the prop on my boat and it came up with a 16 in dia 16 degree prop. I called Cypress Cay and they indicated the boat should have come with a 16 x 13 prop and they will replace it. Just waiting on the dealer to pull it off and send it back now. Kinda curious what I will see for performance or speed increase now?

[killerkernrich]

Is it really harming the motor if the book says 6000 rpm wot and you only get 5000?
Seems to me that would be better than the extra 1000 I would not want to run my truck at wot.

[RcgTexas]

Is it really harming the motor if the book says 6000 rpm wot and you only get 5000?
Seems to me that would be better than the extra 1000 I would not want to run my truck at wot.

yep ! you don't want it running WOT too much but it needs to be able to do that, so you know it is not overloaded with prop. There are consequences for not letting it turn the designed RPM's. Same would be if your truck was not able to turn up its proper R's due to overload.

[Scott1]

Is it really harming the motor if the book says 6000 rpm wot and you only get 5000?
Seems to me that would be better than the extra 1000 I would not want to run my truck at wot.

Yes, same thing they will tell you with a Harley motor cycle, don't lug the engine. That is what you are doing if you are not hitting proper RPM's.

[ron nh]

my 2015 mercury 115hp command thrust came with a 13.25 X 17p. prop.it hits 5,500 rpm's. boat with motor and full fuel=approx 2250lbs. I've hit 5700rpms twice but every other time get's to 5500.I don't know if this will give you any direction, just more info.

[slingshot]

Yes, you are over propped. The problem this causes is called oiling. At 4900 rpm your motor is under the max load allowed by your prop but the oil pump isn't up to maximum circulation it's capable of due to the lower RPM (not good). Your engine should be propped anywhere from 5000 to 6000 RPM. You'll need to decrease your pitch. To get where you want to be just remember that for every inch of pitch you decrease your RPM's increase approximately 200 RPM. So if your spinning a 17 inch prop now and you drop your pitch to 13 inches your RPM's should rise to 5700 RPM given your current WOT RPM of 4900 RPM. You can go to the following site to get a good idea where your prop should be given your make and model of boat.

http://yamahaoutboards.com/owner-resour ... -bulletins

[rancherlee]

which lower unit/115hp do you have? the Standard is a 2.07 gear ratio and the Command thrust is a 2.38 ratio

At 25-27mph I would expect it to run a 13 pitch with the standard lower unit or a 15 pitch with the command thrust lower unit.

[kipper]

I have the command thrust.

[rancherlee]

Kipper, my response was for the original poster, looking at your setup I think that going from a 16x16 to a 16x13 may raise your RPM a little too much. Also If there seems to be no noticeable difference in speed between 3/4 and full throttle you may be getting excessive slip but I really doubt it with 16" diameter prop on a 115hp engine. That 16x13 should be a good heavy load/watersports prop on your toon, If you really feel the need to get it "tooned" in I think a 16x14 would be perfect but see where the 16x13 gets you and it all reality you should have a spare prop on board anyhow.