Tohatsu 6.0 Long Shaft performance . .

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Tohatsu 6.0 Long Shaft performance . .

Postby tattoo on Tue Aug 21, 2012 11:07 am

Tattoo has mounted on its [cutout] transom a 6 hp Tohatsu long shaft. If you just need to get in and out of the marina, then that's a lot more power than you need. But for crusing where you want to get somewhere to anchor or meet others, and the wind and/or tide are adverse, then its my opinion that you need at least 4.5 hp and a little more doesn't hurt. Tohatsu has a 4.5 hp version, but it's identical to the 6 hp except for its compression ratio. The 6 hp is developed at 5,000 rpm using their low pitch prop. My engine maxes out at 4,920 rpm -- so it's very close to its specifications. A higher pitch prop wouldn't reach its rated hp. And the engine pushes Tattoo close to its hull speed starting at a about 4,200 rpm. The lower pitch provides more torque when needed against waves and strong head winds.

I can now report actual measured performance data. At the end of July I cruised from Colonial Beach, Virginia, to Leonardtown, Maryland, to visit my son and family. It's about 17 nm one way. The tide and wind were against me and if I attempted to sail the distance, I wouldn't have made Leonardtown before dark and I'd have missed a wonderful crab feast.

By measurement on my shop's "bathroom" scale, Tattoo used 13 lbs of fuel (calculated as 2.1 gal @ 6.2 lbs/gal). I set the engine to 4,000 rmp and Tattoo usually made about 5 knots. Round-trip transit time was about 7.5 hours. That's about 1.7 lbs per hour. Tattoo's gas tank holds 3.1 gal, giving it a range of about 55 nm. I carry a 1.3 gal reserve of gas in a separate container. If I set her at 3,000 rpm -- the speed would only drop to about 4.5 knots, but the fuel consumption would improve dramatically. Maybe oneday I'll have occasion to get the same data at 3,000 rpm.
Pete McCrary, launched Tattoo Oct '10.
tattoo
 
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