315 Yanmar, RPM & prop questions 28TE

[Cape Codder]

After reading a few posts here, I called Mack Boring, Tech Support in Chicago.
Here is the issue:
I'm not sure of the diameter and pitch of my 4 blade prop, but I'll look this weekend.
I run at around 2700 - 2900 rpm and do aobut 18-19 knots. Occasionally, I push way up to 3400-3500 to 25 knots, and I'm MAXED OUT!!
Bob at Mack Boring advised that the prop MUST be changed. I should be spinning up to 3900-3950 rpm to be right.
We both discussed on the phone that proper cruise will result in something around 3100-3200 to obtain the 18 knot range.
M-B believes that the current prop is putting too much load, and running higher exhaust temps. At 425 hours, and relatively short runs, there is probably no serious damage, but it should be corrected
So:
What prop attains those numbers?
Is ther one for sale out there?
Has anyone had the issue that I have?

Thanks,
Bob

[Capt Ron]

I'm running a 300 hp Yanmar, 2000 28TE. I bought the boat used 4 years ago. It had a 19x19 Michigan wheel on it with a spare 19x20 tucked away. I was over reving with the 19x19, which is ,I'm told is the correct wheel for the boat. My cruise speed was 15-16 knots at 3,300 rpm. The following year I replaced it with the 19x20 spare and got a 16-17 knot cruise at 3.300 rpm. The speeds you're making are making me envious. During the layup I'm having the 19x19 redone and placing it back on for next year. Check back next spring, I'll let you know how it went.

[RicM]

For the second time tonight I'm going to recommend www.boatdiesel.com. The prop discussion there is endless, but the gist from the pros is that amateurs screwing around with their props is their biggest source of repair income. It would seem that by over propping so the engine turns slower for a given speed in knots you would save fuel and wear on the engine, but the opposite is true. Especially with high rev diesels, you are lugging the motor, like driving your car in 3d gear when you should be in 2nd. You will also see scary stories about major engine failures on that site, try to avoid reading them! The regulars are generally conservative types that prefer the low rev designs like the Cummins etc., but it's still a very valuable site.

[RicM]

BTW, I get
2800 RPM 14kts
3000 RPM 16kts
3200 RPM 18kts

I believe my prop is stock all the way, boat fairly well loaded with fuel, water and gear, though I seldom top off the tanks.

I have run 220 hours this first season and averaged 3.17 G/Hour
I am thrilled with this boat.

[Cape Codder]

Hmmm.
More info:
I picked up my winterizing supplies today from Standish Boat Yard in Tiverton, RI. I'm quite sure this has always been Albin's largerst dealer.
I 've known Ken Hilton for years, and he knows Albins inside an out.
I discussed the prop issue, and he said the prop should be a 19x19. If it was more, i.e. a 19x20 or 19x21, then in fact, it could be putting too much of a load.
He said if I did have a 19x19 then the problen is probably the TACHOMETER!!
When he found out I had a Beede instrument panel, he said the tachometers are notorious for being innaccurate, and can be up to 500 rpm off spec!!

Guess what? Whe I got down to the boat this afternoon, sure enough, I have a 19x19. So i'm assuming that it's the tach.
Next spring, Ken said we should use a digital tach, and give her a hard run and check it out. If it's simply an out-of-spec tachometer, the those adjustments can be made.
If it's not the tach, then we can start investingating from there.
Sounds to me that the tach is off just about 400 rpm

[RicM]

The numbers posted above are from my dash tach.
When I had my boat surveyed last Jan-Feb before purchase the tach was witin 100 RPM throughout the range as measured by Johnson Marine Services, so I am pretty confident they are close to reality. Those readings are pretty much what Albin claims in their specs.

[fisham]

I have exactly the same problem as CapeCodder! We have been trying to ascertain the solution for a long time, including the same discussion with Mack Boring! We now also think it is a tach problem...and here is why.

1. The 4 blade prop came with the boat when new...1993 TE. So it is Albin original build.

2. The boat runs at the proper speed in relation to the wide open throttle...ie: at 2800 it runs 19 knots, at 3000 it runs 21 knots and at 3400-3500 (wide open) it runs @ 26+ knots. In neutral it runs to @ 3800 rpm....soooo... apparently all things being relative the tach would be off by about 400 rpm!

3. The boat runs beautifully, does not seem to be lugging, and with boatyard technicians aboard they are impressed with the Yanmar performance.

The idea of a digitach verification is a great one. Next spring first thing we will test out the above theory...I only hope we are right!