Prop for 200 Optimax on SV2100

[captfred]

Hi there!
Finally I could take the "toy" to the water and have some numbers. Just to refresh the info it's a 1993 Sea Pro 220 walk-around with an 1994 200HP Mariner. These tests were performed on a boat that at my best estimate was close to 4,600 pounds.
Before the test I had the cylinder pressure taken The lowest PSI was 119 and the highest was 125. Tested coils, all were shooting strong and installed new spark plugs. Had misaligned oil injection lever markings, but fixed that before testing. Motor seems to be in good working condition except for an indicated high temperature at low RPM's but an impeller/housing kit is on it's way.
Test #1: I took the boat with a 4 blade 15 X 16 prop to San Juan Harbor with pretty flat waters. For what I experienced it was obvious that that size of prop was not a good selection. I'm not that experienced on boating so I'm not sure how to call it, but very often the engine increased the RPM without any additional input from the remote control (I'm not sure if I can call that "cavitation"). Even with that behavior I got 29 MPH out of this setup, but RPM's went beyond 6,000 which is above the factory 5,000 to 5,600 at WOT. (AV plate was not above water but clearly visible from the stern like 1" underwater at WOT and it's height is about 3/4" above the lowest point of the hull's center line with full-in trim).
Test #2: Took the boat out of the water and installed the 3 blade 14.5 X 19 propeller and took the boat to the same spot. Boat planed quicker than with the other prop, RPM was always steady at whichever setting the throttle lever position was selected. It felt like another boat. At WOT I got 37 MPH at 5,500 RPM. I can live with those numbers, but is there any other size of propeller that could give me better performance? Would a SS prop change anything?

Thx!
Fred

[gnrphil]

That's a good improvement, the best thing to do now is get with Ken from prop gods on Band Of Boaters. www.bandofboaters.com/forum/technical-forums/performance-handling
What he doesn't know about props isn't worth knowing.
You still might want to raise one hole.

[freezerfiller]

Jan 21, 2017 21:35:20 GMT -6 captfred said:

Hi there!
It felt like another boat. At WOT I got 37 MPH at 5,500 RPM. I can live with those numbers, but is there any other size of propeller that could give me better performance? Would a SS prop change anything?

Thx!
Fred

Fred, A SS prop has less flex than an aluminum prop at high load, so it's like a little more pitch but not much. Was the 37mph @5500 rpm your WOT? If so, You are probably about right. Can you optimize it? Sure! It all depends on how much money and time you want to spend. I agree with Phil, you might want to try taking the motor up a hole. That won't cost you anything but a little time and might get you a few more mph and better mpg. If it starts to cavitate, you can always move it back.

[captfred]

Thx guys!

I'm very grateful for your advice. My sailing will be mostly over choppy water (no big lakes around, just open sea) so I'm sure it won't be that often we'll be cruising at WOT. I wouldn't subject the boat and passengers to that environment for long periods of time. I'm totally convinced on the logic's of a higher motor, so my final question before moving a hole up is, if while on choppy water a higher motor will suck air into the prop due the up/down movement and decrease performance, affect cooling or damage the motor for excessive RPM?

My previous run before the testing at current propeller height, over 3 to 5 seas and a heavy boat, was awful listening to the RPM variations and having to adjust throttle (I'm aware I got the wrong prop).
Now...
If the higher motor applies to both, flat and choppy waters, I will definitely do it very soon (there's somewhere in my garage a cartridge of 5200 waiting to be opened).

Sorry for you boys, but I'm a "question machine". Hope you don't get annoyed. Ha ha ha!!!

Thx again!

Fred

[Juan]

Mounting your motor in a hole higher might help your performance when the motor is trimmed correctly then you can trim the motor down in rough seas and it shouldn't suck air.

[freezerfiller]

There is a possibility that by raising the motor it could cavitate, but it is more likely to do it when it is trimmed out or in a turn. If you experience this just trim it back down, and that should get you through the day until you can get it moved back to the lower hole. Obviously if you are having issues with high rpms, or not seeing a good water stream, stop. But usually you will hear the exhaust volume increase dramatically before that should happen. BTW, once you open it, that 5200 lasts a long time if you keep it in the freezer. Don't sweat the questions, that's what this place is for!

[captfred]

Well, up a hole it is!!!
I'll do the job as soon as I have the time and come back with the results. I'd never thought of putting sealant on the freezer. (Actually your nickname is giving me second thoughts on it. Seems like you want to get everything in the freezer, je je je!)
Thx guys!
Fred