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508Re: New member

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  • Oliver
    Dec 2, 2011
      --- In privateer20@..., "seannorris65" <seannorris65@...> wrote:
      > hi all
      > I have a 6 hp tohatsu on my one which came with the boat. As I have my boat in a relatively light trim my own view is that it is too big as the boat seems to reach max speed at just over half throttle. If I had too replace the engine I wo
      > would probably get a 4hp.

      Several points here.

      First, on your description of the engine reaching maximum hull speed on between half and two-thirds throttle (in smooth water) this suggests that your power is about right for smooth water. You don't really want to thrash the engine by running it for extended periods at full throttle, and neither do you want the associated fuel consumption. So cruising at between half and two-thirds throttle, while still maintaining maximum hull speed, sounds to me about right.

      Second, never underestimate the extent to which a combination of head winds and a head sea can sap the power of an engine, and dramatically reduce available boat speed.

      I have a 5 h.p. Honda, complete with charging coil. To my mind this is both an expensive option and a heavy one, but for my use I think it is worth the expense and weight.

      I do aim to do moderately extensive coastal cruising, so the ability to recharge the battery is useful, even though this is hardly an efficient means of doing so. I intend to also explore other methods of recharging it.

      As a means of alternative propulsion, which is its primary purpose, the key test is what speed I can achieve to windward in half a gale and with a head sea. (If conditions are kinder, and time is not pressing, I would of course usually be sailing rather than motoring anyway.) I may of course wish to moderate my speed on account of the sea state, but if punching a foul tide and if the sea state is not too bad the ability to still make good progress is sometimes very valuable. On the basis of that test, I feel that 5 h.p. is about right.

      By way of hard data, my current engine (almost brand new, only just run in, a replacement for a slightly older one of the same model which was stolen last year) will comfortably achieve close to 6 knots in smooth water, and I doubt that it is yet developing its maximum output. However I have occasionally been down to about 3 knots in head winds and big head seas and with three adults aboard, even with the motor running hard.

      My previous motor, well run in but still reasonably young, on one occasion achieved over 6 knots to windward into the teeth of force 6, albeit that this was only in the Mersey (and not in the "vertical walls of water" parts!) and with just myself aboard.

      My previous yacht, back in the seventies and eighties, was a 1912 heavy 25-ft gaff cutter with an 8 h.p. inboard diesel, turning a nice big 3-bladed propeller. This would reliably give a little over 5 knots in smooth water, and would reliably push to windward if necessary in dirty conditions, but I do remember one horrendous passage into head seas left over from a sustained gale which had kept me lying three days storm-bound in port, when the best I could achieve even with the engine running flat out was a knot and a half - and this on a single-handed passage home of around 40 nautical miles!

      I think if I had a 2.5 to 3 h.p. engine on my Privateer I might well make do, and live with it, but no way would I now downsize the 5 that I currently have to anything smaller.

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