Looking for performance comparison - 1999 Bimini 306 w/ Ox66

[IFish4Tuna]

Hi I'm looking to compare numbers w/ someone w/ a similar setup. I would be interested in hearing from either Marlin or Bimini 306 owners running the SaltWater Series OX66 2 stroke engines. Yes I know the engines are old, but they only have about 1100 hours, and have been well maintained. I have been chasing performance concerns, and have a very long thread going on THT.

I am getting no where near the performance quoted on the performance bulletins for either Marlin or Bimini. On a good day I get .9 MPG, and 35-36 WOT at 5300 RPM, and am not getting the RPMs I think I should (5400). I'd really like to compare w/ Grady Owners. I am getting about 32% prop slip.

I am launching the boat tomorrow with new 19" Power Tech props. The original props have had various repairs done over the years and are out of balance. So tomorrow's test run will be interesting, but I'm not optimistic on significant positive results.

I normally run the boat heavy (fuel, people, live well) for offshore trips. I know the factory recommends the Marlin use the 17" prop and the 306 use the 19".
I have contemplated trying the 17" prop also. The engines are installed in factory hole #1, and as such the cavitation plates when level w/ the hull are below below the hull. Not visible while driving at cruise. Would be curious if any GW owners have raised to 2nd hole w/ more positive results.

Ed

 

[IFish4Tuna]

Re: Looking for performance comparison - 1999 Bimini 306 w/

Attached are my numbers w/ my new power tech 19" props.

I think there is room for improvement. The RPMs are on the low end at WOT. I'm concerned the engines are being over worked.

 

[DennisG01]

Re: Looking for performance comparison - 1999 Bimini 306 w/

The AV plate should be just barely skimming across the surface. It sounds like you're a bit too low. I would start by raising the engines and get that sorted out first, before doing too much with props. After you raise the engines to the proper level, then fine tune with the props.

 

[IFish4Tuna]

Re: Looking for performance comparison - 1999 Bimini 306 w/

Thanks.

I realized my spreadsheet did not include the full model under test.

its OFS 3 (3 blade)

After speaking to power tech, they recommended a 15.25x16 4 blade. Given I normally run w/ heavier loads and to help w/ fuel econ and keep on plane in rougher offshore weather. I'm all about cruise, don't care much about top end other than to know the prop is sized accordingly for WOT.

 

[Tuna Man]

Re: Looking for performance comparison - 1999 Bimini 306 w/

I know this is not the same boat or the same engines, but might help as a reference. In addition, I can't stress enough that my boat bottom was very smooth. I suspect your engines sit a little too low and the hull may not be very smooth?

viewtopic.php?f=2&t=17440&hilit=+mpg

 

[Tuna Man]

Re: Looking for performance comparison - 1999 Bimini 306 w/

More prop results just for a reference:
viewtopic.php?f=3&t=14837

Btw, I did end up raising the engines and gained very little performance wise (maybe hole shot is a little better but that does not matter to me).

 

[seasick]

Re: Looking for performance comparison - 1999 Bimini 306 w/

is your hull bottom painted? The factory tests are done with unpainted and clean/ waxed hulls.
As you probably know, the SX motors are gas hogs. You didn't say at what revs and speed you get .9 mpg but for the age of the motors and hull the number seems to be in the ballpark. The load carried is important. You can't make an apples to apples comparison to the factory specs if you don't carry a similar load ( including people, gas, water and gear.
The WOT revs are in the range spec'd by Yamaha as I see it.

 

[family affair]

Re: Looking for performance comparison - 1999 Bimini 306 w/

I have gone through a similar exercise on our boat and ended up going back to the factory 3 blade. Grady mounted the engine very low on our boat. We now have the highest hole possible and the AV plate is still buried. The 4 blade was actually worse because we can't get the blades high enough out of the water to get the drag reducing benefit of the 4 blade. We don't have bottom paint, but chalked up the discrepancy to ethanol fuel, a reworked prop, and fresh water operating.
As for WOT, we can get there or better than the original performance report with a similar load.

 

[seasick]

Re: Looking for performance comparison - 1999 Bimini 306 w/

I have gone through a similar exercise on our boat and ended up going back to the factory 3 blade. Grady mounted the engine very low on our boat. We now have the highest hole possible and the AV plate is still buried. The 4 blade was actually worse because we can't get the blades high enough out of the water to get the drag reducing benefit of the 4 blade. We don't have bottom paint, but chalked up the discrepancy to ethanol fuel, a reworked prop, and fresh water operating.
As for WOT, we can get there or better than the original performance report with a similar load.

As I understand it, all other things being equal, 4 bladers add more drag than 3 bladers. I don't understand you comments about getting the 4 bladder higher.
Also note that if a set up allows the motor to rev higher than the WOT specification, that is not a desirable thing. It usually means (but not always) that the prop is undersized.

 

[IFish4Tuna]

Re: Looking for performance comparison - 1999 Bimini 306 w/

is your hull bottom painted? The factory tests are done with unpainted and clean/ waxed hulls.
As you probably know, the SX motors are gas hogs. You didn't say at what revs and speed you get .9 mpg but for the age of the motors and hull the number seems to be in the ballpark. The load carried is important. You can't make an apples to apples comparison to the factory specs if you don't carry a similar load ( including people, gas, water and gear.
The WOT revs are in the range spec'd by Yamaha as I see it.

Yes - painted bottom. Thanks for pointing out the benchmark is with an unpainted hull. That likely affect it some.
In my first table at the top. The .9MPG was on the old reworked propellers. It also shows RPM & Speed.
My load was similar to the benchmark
The WOT are in spec, but on the low end. Max is : 4500-5500. And with the new props they are WOT at 49. I've read repeatedly that the RPMs should be on the upper 1/2 of the range. I'm in the lower.

I am going to move the Engines up 1 hole once the marina can squeeze me in.

Thanks for taking the time to reply.

 

[IFish4Tuna]

Re: Looking for performance comparison - 1999 Bimini 306 w/

More prop results just for a reference:
viewtopic.php?f=3&t=14837

Btw, I did end up raising the engines and gained very little performance wise (maybe hole shot is a little better but that does not matter to me).

Interesting. Thanks.
Your numbers look good. You must be pleased.
Thanks for replying.

 

[family affair]

Re: Looking for performance comparison - 1999 Bimini 306 w/

As I understand it, all other things being equal, 4 bladers add more drag than 3 bladers. I don't understand you comments about getting the 4 bladder higher.

A properly set-up 4-blade will run partially above the surface of the water. By doing so you will have less blade surface in the water (at cruise) compared to a 3 blade that must always be 100% submerged to prevent blowout.

My WOT is the same as Grady, but my speed is higher, likely from the cupping on the reworked prop. Yes, excessive rpm will be bad if you run beyond the recommended rpm, but sometimes an easier to turn prop is a better way to go. For example, if you run heavy regularly, a smaller prop will make it easier to get out of the hole and make the engine not strain while cruising. The risk is running wot with a light load and over revving.