Mark, Very cool that you have that info. How did you arrive at the power requirements? (don't just tell me: MATH) :) Bill Makin' Time M17 #622 On Fri, Mar 4, 2011 at 11:08 AM, Mark House <itsmark@bresnan.net> wrote:
Karen & Smiley:
I have some info in my archives about power requirements for displacement hulls that might prove helpful.
M-15 13.3 ft. LWL, 4.89 Knots Max, 750 lb + 600 lb. load 3.5 knots needs 0.26 HP, 4.5 knots needs 0.73 HP
M-17 15.83 ft. LWL, 5.33 Knots Max, 1600 lb + 600 lb load 3.5 knots needs 0.33 HP, 4.5 knots needs 0.73 HP, 5.0 knots needs 1.76 HP
At max. hull speed both need around 2.7 HP as they try to climb their bow wave.
The point is that we really don't need all the power we usually put on our boats. Of course, wind drag adds to the power requirement, props are not perfect, and neither are engines. In my experience, motoring out a narrow channel into strong prevailing wind, the biggest factor is lifting the outboard prop out of the water in 3+ ft. chop. I once owned a San Juan 23 that got blown 90° off course by 25 knot winds when the prop lifted out. I had to make several 360° turns to have another go at the waves until I could fall off and raise the sails. I use a 4HP Suzuki with 20" shaft on my M-17, but wouldn't hesitate to buy snaller next time. I think the Tohatsu 3.2 with 22" shaft would be a great choice. I wouldn't know, but the longer shaft might make the prop drag when lifted and sailing.
Mark House #232
----- Original Message ----- From: "Karen and Smiley" < magoo252@comcast.net> To: "Montgomery Sailboat Forum" <montgomery_boats@mailman.xmission.com> Sent: Friday, March 04, 2011 5:02 AM Subject: M_Boats: M 15 transcom heights
Would one be better off using a shaft length of 22 inches as found on the Tohatsu 3.5 hp outboard as opposed to the 20 inch high shaft lengths of most long shaft outboards. Additionally from what I am used to on my P21 which I had driven using a 8 hp 2 stroke I felt that I never could get most of the power out of that engine to making Hull speed at about ¾ throttle. So I assumed that 2.5-3.5 hp would be just right for the M15 with 2 hp being maybe a bit shy for those BAD days when you need to boogie from a storm. Thanks
What is the trick to re-fueling when you're out in bumpy waters BTW
Smiley
magoo252@comcast.net
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