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Old 18-06-2009, 17:34   #1
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Question Engine Usage

first, thanks to all who have been filling in the gaps between my reading of books and my lessons. even though i can ask my instructor i like getting different readings on topics.

moving on, should the engine be powerful enough to actually cruise (and if so how long/far) or just to troll/idle through channel and for docking?

thanks in advance.

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Old 18-06-2009, 18:25   #2
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Sorry but I think we need to know what type and size of boat are you looking at, and of course, what you are intending to do with it. There's considerable difference in terms of power requirements between...say...a tailerable sailboat verses like..a 50' Cat or Tri...or a even 45' mono set up for offshore cruising.

I'm not an expert on this, but its pretty much a given for cruising sailboats that they have a designed hull speed (a formula having to do with length and beam on the water line, keel size etc. etc)...and most cruising general...appear to have an engine that should push the boat close to that calculated speed. I say most, because there's always lots of exceptions. We have a 41 foot sailboat that the iron-Jenny will push at hull speed of about 7.5 to 8 knots...which is the design calculated hull (sailing) speed. (Of course it's slower if we're going up hill but that's another topic)...I don't know how fast we can really go because with the sails up and engine running we jump to Warp Speed and our gauges are not set up for it...although I have seen Marlin trying to keep up with a plug I was trolling once and I figured it was pretty fast because he burned off two fins just trying to catch up to the bait... but I digress....there are people out cruising who don't even have an engine which tend to make the rest of us look really bad sometimes.

On a more serious note...In the channels and docking I think you only need enough power to overcome wind and current...our motto on Pure Joy is slow is good...slower is better and if you're able to dock with no engine running at all...that's a Royal Flush! OTOH I've seen people who can't make it into the dock or down a channel without a thousand horsepower...go's not what you's how you use it.

Ray and Sandy
S/V Pure Joy
Olympia, WA

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Old 18-06-2009, 19:12   #3
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Aloha Florida,
As you mentioned in another thread that you were thinking of powering a 25? A 6hp will push you to hull speed which is the maximum you will be able to go. For a little extra against wind a 7 to 8 will do. Your primary form of propulsion is sail so the auxiliary is only in the event you have sail problems, need to go directly into the wind, run out of wind or have to dowse your sails in order to go into a downwind slip and you haven't figured out how to do it under bare poles.
Those who sail without engines many times need to rely on others for a tow or are extremely patient when the wind dies. Others of us have deadlines and sometimes need to be someplace by a certain time. That's when an engine comes in very handy.
Hope you can find your answers.
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Old 18-06-2009, 20:03   #4
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what i'm looking at are between 23-28ft monohulls, which takes between 6-8hp, right?

most of the boats i'm looking at have outboards. what i don't know is what exactly their function is; what type of workout they get.

i did not know if you could just use the engine for whatever reason and for how long is the engine suppose to function at that output.
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Old 18-06-2009, 20:24   #5
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6hp is fine for 23' and 8hp is somewhere between fine and adequate for 28' IMHO. It's nice to have a few extra hp for punching through a steep chop (against tide and current, of course).

The outboard motor that propels smaller sailing yachts is used for much more than simply putting in and out of the slip/channel, the same way an inboard diesel is used for motoring long distances: it's all up to the whim of the skipper.

Outboard motors can be run for extended periods, assuming adequate fuel supply. Regular periodic maintenance will maximize the hours of life it will deliver.
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Old 18-06-2009, 20:58   #6
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The prop makes a big difference as well. Our boat has a 10hp Volvo (25 feet) and displaces about 4500lbs. With the original folding prop she was a pig.

We installed a MaxProp and it's like a completely different propulsion system.

Length, displacement, prop hull cleanliness all count.

I don't think I would go less than 10hp for a 25 foot boat.
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Old 18-06-2009, 23:09   #7
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guys, I think he's asking a more general question -- what do you use the engine for on a sailboat? Answer: most cruisers spend more hours on the water under engine power than sail, even though we would all prefer to be sailing all the time. Motor for:

1. Getting in and out of the marina

2. In channels and other tight spots where you need more control.

3. When the wind is on the nose (most cruising boats can't sail in directions representing nearly one-third of the compass, so the wind often seems to be 'on the nose').

4. When the wind dies.

5. In heavy weather and big seas, to help maintain control.

6. While anchoring.

Did I leave anything out? In real life it's the sails which are auxilary; motor is really primary propulsion system for a cruising boat.
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Old 19-06-2009, 01:20   #8
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For all the activities above, would like to confirm previous posts that size matters. If re-powering, get the biggest engine that will fit in the space provided. On existing setups that don't have the extra hp, get the best prop to deliver the available power where it matters.

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Old 19-06-2009, 08:36   #9
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For me its most important role is that of a piece of safety equipment.
It should be powerful enough to get me out of trouble with heavy wind, current and waves are on the nose.
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Old 19-06-2009, 11:17   #10
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Florida Newbie,
Rule of thumb, you want 1 horsepower per 500 lbs. gross weight
(boat, tankage, gear and crew) For reasons well stated in above posts,
motor should be able to run for extended period if need arises.
Condition/maintainence of motor and adequate fuel supply are important
even if you are ony daysailing.

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