overloading

[halfmoon]

Previous postings have stated that all Yanmar powered 28s used a 2:1 reduction gear. But, Serenity is a re-power. Does it have that 2:1 ratio? Spoke with Max's prop folks yesterday. They found my 19x19 four blade difficult to believe. I find my performance hard to believe! Ready to buy a new prop, but need to be sure transmissions have the same reduction ratio.

[RobS]

The Yanmars are all 2:1 (please correct me if I'm wrong). That results in a theoretical speed almost identical to his actual speed, like 3% slip.. ?

[RobS]

Yes he was a repower from a Penninsular. Penninsulars should have had a 1.8:1 gearbox which would then calculate to be approx a 12% slip, much more sensible... If it were possible to using the existing gearbox, that I am not sure of.

[Cape Codder]

Hmmmm! (Scratching my head)
RPM:3800
Gear ratio: 1.8:1
Pitch: 15.25
Slip: 10% (estimated)
Estimated speed: 27.44 mph/23.84 kts

[RobS]

Pitch = 16.25 (for a cupped prop add 1 to the Pitch)

[Serenity]

From the records that I have, the transmission is the same one that came with the Penninsula 300. Hurth HSW630-V1. Attached is a photo of the prop before I installed it . From what B&S told, that the 3 blade prop I have has as much surface area as a 4 blade.

[halfmoon]

My quick search on the Hurth HSW630 V1 transmission results in the finding of 1.56:1 reduction ratio. So, this is much different than the standard 2:1 on the factory installed Yanmars. The magic prop will not work with my drive.

[RobS]

My quick search on the Hurth HSW630 V1 transmission results in the finding of 1.56:1 reduction ratio. So, this is much different than the standard 2:1 on the factory installed Yanmars. The magic prop will not work with my drive.

The Hurth tranny model number does not indicate the gears that are in it. The tranny will have a tag on it

[halfmoon]

Thanks, RobS. OK Max, what does your tag reveal?
Note: 2007 post by GeryGarcia reported a 1.57-1 ratio for his Peninsular and Hurth.

[Serenity]

OK OK OK I will go down to the yacht with my trusty LED flashlight and take a gander. I prefer the "magic prop" theory. I am planning to take my honey out tomorrow with a witness. She may be ugly, but she can sure cook.

[Serenity]

The tranny has a 1.56 reduction. The engine is a 315 Yanmar with 200 hours on it. The current owner was in HS when JFK was shot, saw the Beatles on the ED Sullivan show (Black and White TV), remember the song " Can't get no satisfaction" before I went in the Navy, took my drivers test on a 1962 Rambler station wagon, and didn't realize diesels didn't have spark plugs till 1979 when I purchased a 1974 Luhrs with a 165 Perkins Turbo Diesel. Serenity runs great and handles just as good with the "magic prop".

[Serenity]

OK, I took Mike out today from Sweetwater and he will confirm my numbers. Got me guys. I just drive the boat.

[sweetwater]

It's true all right. Either that or the ride to kismet is down hill... Both ways. We were cruising at 22 plus and topped out around 30. Knots. But I still think serenity uses the less common Yugoslavian knot.

[Cape Codder]

OK!

RPM: 3800
Gear ratio: 1.56:1
Pitch: 16.25" (adding 1" for cupping)
Prop slip: 7.9%
Speed: 30 kts.

It actually IS possible.

When I'm back in the water, I'll test Santosha.

RPM: 3950 (I hope)
Gear ratio: 2:1
Pitch: 18" (just re-conditioned by H&H)
Slip: 8%
Theoretical speed: 27 kts.

[RobS]

Any cup Bob?