Perkins 4.108 OR Yanmar 3HM30F?? Tayana 37

[bletso]

Let's see if I get this correct. Horse power and torque are a function of the engine specs. Prop diameter is selected basically for the horsepower available. The pitch is then selected to allow the engine to match its HP/torque values at the optimum value for the engine. Over propping can over time damage the engine and under propping won't load the engine to get its peak performance curve.

You will see more torque at the prop shaft, but you will still be limited by the HP the engine can deliver. The different transmissions will alter the pitch you will need, but overall performance will be basically the same. Kind of up one and down the other.

[lancelot9898]

Just one correction to the original post. I bought my T-37 new back in 1985 and the standard install was the Yanmar. I had mine upgraded to the 4-108. It came with the 17 by 11 fixed blade prop which I never used since I installed a max prop from day one. It was a 17 inch max prop and adjustments were made to the pitch several times to get the performance that I desired. Both the 4-108 and the max prop are doing fine after 30 plus years.

[Cheechako]

The prop diameter is usually defined by the clearance to the hull or other boat structure. (often 15% of diameter, rule of thumb) The bigger diameter the better. Then adjust rpm as needed with pitch.

[Panos]

I have a Tayana 37 with a 39hp new Yanmar 3hj4e installed by PO. I cruised a lot and crossed the Atlantic ocean 3 times with her. Most of the time I sail but when motoring I never run the engine faster than 2100 RPM. At this speed the Yanmar produces only 33hp. So I guess that a smaller engine would be just fine and you would run it at the nominal speed, as recommended by the diesel experts.

PK
S/V Cookelu meu, Tayana 37

[Cadence]

I like running at 75% of rated RPM and if set up right attaining hull speed at that. However goosing the engine occasionally is needed to blow out carbon and prevent ridges in the cylinder walls. MHO

[Wainui]

What RPM do you guys run the 4108 at?
I run at 2400 which gets me 6knts at 1.3 gallons per hour.
Wide open is 2900 in gear.
26k lbs boat.

[lancelot9898]

My tach is reading 2500 rpm at cruise (6 knots) and wot is 3000rpm (7 knots)
HOWEVER, the tach is reading high according to calibration with a photo tach.
Not a linear relationship but the true rpm is closer to 1900 at cruise and the wot is 2300.
fuel usage is around 0.75 gal/hr

[Panos]

In flat waters and at 2100 RPM I get 6 to 6.3 knots and the consumption is 0.7 gals/hour (2.5 liter/hour). My boat is a Tayana 37 equipped for long term cruising, weighting 23000 lbs (about 11 tons), and the engine is a Yanmar 3jh4e, new in 2006 now has about 3000 hours.

Panos

[lancelot9898]

I think the design weight of the Tayana 37 was 24000lbs(or maybe it was 22000), however on the travel lift mine weighed in at over 30000. Travel lifts are known not to be too accurate so I take that with a grain of salt even though I'm about 2 inches down on the design waterline.