CS 20 motor size

[Noklin]

I know that the less weight hanging on the transom of a sailboat the better, so I am planning on using a light weight 5 HP motor on my CS 20.

In an earlier post, it was stated that a CS 20 could not handle a 35 HP outboard (more motor that I would buy, but in this case it was free).

This made me wonder how the recommended motor size for a boat was determined. If there is only a 5 pounds weight difference between a 15 HP and a 25 HP motor, why is the 15 HP recommended? Assuming the transom is strong enough to support the weight and force of an outboard, what other factors determine how large a motor can be used on a boat? How much difference is there between what is legal and what is reasonably possible to use?

[kmrmike]

Nolkin, I found the following on the web. Hope it's helpful"The maximum horsepower capacity marked on a boat must not exceed the horsepower capacity determined by the computation method discussed in paragraph (a) of this section. (a) The maximum horsepower capacity must be computed as follows: (1) Compute a factor by multiplying the boat length in feet by the maximum transom width in feet excluding handles and other similar fittings, attachments, and extensions. If the boat does not have a full transom, the transom width is the broadest beam in the after most quarter length of the boat.

(2) Locate horsepower capacity corresponding to the factor in Table 183.53. (3) For a boat with a factor over 52.5, if the horsepower capacity calculated in Table 183.53 is not an exact multiple of 5, it may be raised to the next exact multiple of 5. (4) For flat bottom hard chine boats with a factor of 52 or less, the horsepower capacity must be reduced by one horsepower capacity increment in Table 183.53.

Table 183.53--Outboard Boat Horsepower Capacity

[Compute: Factor = Boat Length X Transom Width]

If factor (nearest integer) is.............. 0-35 36-39 40-42 43-45 46-52

------------------------------------------------------------------------------------------------Horsepower Capacity is.............................. 3 5 7.5 10 15

[Joe Nelson CS#35]

My little 4 HP will push me at 8 mph. You also need to consider the strain of a motor hanging and bouncing off the transom while trailering. I would install the lightest motor you can get in the 5 hp range or less. One of those little 2 hp honda 4 strokes would be sweet. My 4 horse is an older 2 stroke, but only weighs 30#. The smaller motors also use less gas. If you do any cruising and the wind dies, you will be glad that you get good fuel economy. On my last cruise...25 miles...I took enough gas to get me back and forth without any wind. You never know. If you start calculating fuel needs for a larger motor, you are going to be packing a lot more fuel, when the space and weight might be better served with stores and gear. I frequently take 5 people with gear for camping. I am always looking for ways to reduce payload.