Westsail Owners Alliance - Thread: "Perkins 108 Cruising Speed"
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Thread: "Perkins 108 Cruising Speed"

12,268 posts on 2,444 threads   •   From Mar 07, 2004 - Jan 08, 2012

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Perkins 108 Cruising Speed


Dick and Libby Mills

I've only owned Tarwathie, my Westsail 32, for a few months, so I'm still learning her "normal" characteristics. While she sails beautifully, I'm frustrated by her performance under power with the Perkins 108.

I can only sustain 1800 RPM continuously without exceeding 220 degrees coolant temperature. I get 1 knot per 1000 RPM, so my top cruising speed under power is 3.8 knots. In costal waters with strong tidal currents, that's unsafe.

I've hired two mechanics and we've been through everything in the raw water and primary coolant sides. We cleaned, backflushed, replaced impellers and removed the thermostat. Still the problem persists.

I talked with a Perkins engineer. He said that a tip-top condition coolind system should allow cruising speed at 80% of full-throttle RPM. For me that would mean 2,500 RPM. I'm surprised by the 80% number. Why isn't it 100%? I never owned an engine before with performance limited by the cooling system.

What I lack most is a calibration point.

What do other Westsail 32/Perkins 108 owners achieve for cruising RPM and speed?

Has anyone else experienced problems similar to mine?

Has anyone tried modifying the Perkins with an oversized heat exchanger?

Any information would be appreciated.

Thanks,
Dick Mills


Bud Taplin
(Member)

Dick, Sounds like the problem may be the incorrect prop pitch. Also, the 80 percent number is the correct one to use when you have the correct prop. I will email you the page from my Westsail Service Manual regarding engine and boat speeds.


Michael Dougan

1800 RPM is the speed my boat's PO recommended as top cruising speed... at that RPM I can get between 5 and 6 knots with my Volvo MD11C. So, with the same hull and same RPM you should be able to do as well... I have a fixed three bladed prop, but don't know what the pitch is.

As an aside, my boat's PO put in an oversized heat exchanger and I always run under 200 degrees (assuming my temp guage is working!).


Frank Butler (Guest)

I can run the 4-108 in Intuition W32 #0825 @ 2400 RPM continuously without overheating. Usually pushes her along at about 5 kts. I can redline her for about 20 minutes before getting excited about overheating. In addition to checking the prop pitch, you might consider having the heat exchanger cleaned. Don't forget to replace the zinc in the heat exchanger.

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