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Old 10-02-2008, 22:11   #1
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is 13 hp yanmar too small for 33ft steel yacht?

Hi to all
Im new to this forum and was wondering if anyone would give me their opinion regarding a yacht that I am looking at.
The yacht is 33 ft, steel construction, weighs 4.9tonnes and is powered by a 13 hp yanmar.
I have sailed on a 25 ft fibreglass yacht with a 8 or 9 hp bmw and the 250 nm voyage was slow going when with out wind at about 4 knts
The broker states that the yacht Im looking at will make 5 to 5.5 knts.
Questions
Does 5 to 5.5 knts seem optimistic?
Is this motor too small for me to do comfortable coastal cruising?
Thanks for helping
neil
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Old 10-02-2008, 22:32   #2
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Hi Neil. In calm conditions you will most likely get upto 5kts. But in any wind or lumpy sea condition, I would say you are pushing it up hill. The ruff rule of thumb of 3Hp per tonne puts it about right on the money for power to weight. But I find it hard to believe a 33ft Steel hull weighs in at only 4.9 tonnes though. You sure it is only that weight??
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Old 10-02-2008, 22:35   #3
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I think your instincts are correct and you're right to be concerned. While 13 hp will probably be just fine for leaving your slip on a perfect day, there are times when there's no substitute for hp.
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Old 11-02-2008, 07:04   #4
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I had a 12hp yanmar in my C-30, just as mentioned it was fine for motoring in and out of the slip and anything in decent weather, but anytime we had strong current or wind we sailed or motor sailed.
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Old 11-02-2008, 07:25   #5
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my 20 foot 2.5 ton boat uses a 6 hp outboard mounted in an engine well, essentially making it a saildrive for most intents and purposes. For calm days it's great, I've gotten 6-6.5 knots out of it at full throttle. I've had it out in some rough weather too and while it didn't move use fast, it did move us and got us home.

for your boat if the weight is correct, it seems that you're doubling the weight and doubling the horsepower from my example. you are not however, doubling the length. just judging from rough estimates and my experiences I'd guess that about 5 knots would be normal on a calm day. I'd guess maybe 1-3 in pretty choppy conditions nose straight into the wind. Again, just guessing, but I'd assume that the engine would be little if any help if the wave height exceeded half the boat length.

If you stayed in protected waters and if you were to venture out of them you were careful to listen to the weather for anything severe, it'd probably be fine.
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Old 11-02-2008, 08:01   #6
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13hp would be a dream compared to no engine at all, but you will be significantly restricted. Have you gone out in this boat? Go out on a windy day and find out.
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Old 11-02-2008, 09:33   #7
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My 32' Ontario has a 13hp Yanmar for a bit over 11,000 lbs displacement. It can definitely be slow going against any noticeble tide or current, but it does go.
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Old 11-02-2008, 13:54   #8
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The biggest worry is channel work . If you are under powered and are using your engine because you have the wind on, up a channel then be careful. The boat gets slower as the wind picks up until........horror you lose all steerage. You have one two choices 1. get the anchor out and fast...or 2. try and bring the bow around and go back the other way. In practice if its safe enough to anchor then its probably safe enough to tack..and with 2. you had better hope that the way the boat bears off is NOT towards the shallow side of the channel. I speak from many years of experience. I have 7.5 HP in 30 foot 3.5 tons. My new boat has 53 hp !
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Old 11-02-2008, 15:41   #9
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Powering a vessel to close to hull speed takes very little HP if the vessel is propped correctly and the bottom is clean. I'll bet that I could push that boat to 6kts with an inflatable and a 15hp O/B with relatively no problem (if it has a clean bottom). A properly running 13hp inboard should have no problem pushing a sailboat at 5.5-6kts. in calm conditions.

When you get into choppy waters, the vessel will be slowed every time that she hits a wave but if you have choppy conditions, you also have wind and should be sailing anyway.

Current does not enter the equation because even if you are in a 4kt current, you will achieve 2kts over the ground. If you had a 30hp engine, you may achieve and addition 1 - 1 1/2 kts. Current (by itself) won't lower your speed through the water.

Where you may have difficulty is if you are trying to enter a harbor (as mentioned above). Then you may need to put up the main (sheeted in tight and motor sail, tacking up the channel. In severe conditions, you may have to wait outside but I would say that would be pretty rare unless you are in a very wind prone area.

The boat is obviously under powered but I wouldn't consider it unusable by any means. As stated above, it's a heck of a lot better than no engine at all.
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Old 11-02-2008, 15:43   #10
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I think this engine is way too small. I have a 30 horsepower Yanmar in my trimaran which is the minimum for a lightweight multihull carying a bit of kit. I suggest the same engine as I have will weigh about twice as much or a bit less and will give you good economy with a little power in reserve. You need at least twenty Yanmar horsepower in your boat--and I would go the extra. Imagine a gale has you trying to claw your way off a lee shore. You need the extra horsepower when something rips--and your life has to be worth more than the cost of a new engine, gearbox and a good folding propellor.

I might find it easier to look for a larger engined vessel in the first place--but a new engine does give one about ten years of use if one is careful and maintains it properly.
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Old 11-02-2008, 18:16   #11
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7hp, 7 tonne...

I put a 7hp Yanmar into the Hartley RORC 32' that I built.

It was a while ago now and I only "cruised" Sydney Harbour and Broken Bay but I seem to remember that the boat went quite well with it (5 kts VDO?).

I can see the point that motoring against the current into a strong headwind and a chop would be problematic but most boats would be difficult under those conditions.

If you can accept this then it depends on what the rest of the boat is like.
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Old 11-02-2008, 21:38   #12
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Well--I see that thirty or so people have just been winched to safety from exactly the same spot I was caught by a sudden blow against a lee shore--on Hook Island. It looks like the vessel is lost--I am waiting to finsd out why they were unable to motor free of the place. Perhaps--as sometimes happens--the diesel failed them when it was most needed. Perhaps it was not powerful enough to turn the vessel into the wind.

I will just have to wait and see.
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Old 11-02-2008, 23:09   #13
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The boat looks like it has a heap of windage from the pics......http://www.abc.net.au/news/stories/2...9.htm...really crappy weather up there at the moment and the forecast is not brilliant either. Whats the saying "Queensland, "raining one day, horrible the next" or my new favorite . " If you have a tan you spent the summer in Melbourne !!!" : )
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Old 12-02-2008, 02:10   #14
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My boat is 12 1/2 tons and came with a 23hp volvo...As stated by most here...It got me in and out of my slip. Although I would have to reverse really early to prevent stabbing the boat across the way with my bow sprit. I repowered with a Yanmar 4JH(44hp). It's perfect so I would agree with wheels numbers.
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Old 12-02-2008, 11:05   #15
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Quote:
Originally Posted by Celestialsailor View Post
My boat is 12 1/2 tons and came with a 23hp volvo...As stated by most here...It got me in and out of my slip. Although I would have to reverse really early to prevent stabbing the boat across the way with my bow sprit. I repowered with a Yanmar 4JH(44hp). It's perfect so I would agree with wheels numbers.
I don't think that your "Stopping" problem was due to a lack of HP. That is usually a matter of having a poor prop (Foding, 2 blade etc).

If I were going to have a vessel that was under-powered, I would strongly consider a Maxi-prop (or similar) or at the very least a well pitched 3 blade prop. The prop will make a world of difference on a vessel like that. The critical thing is to be sure that you can get max RPM out of the engine without being able to over-rev the engine while motoring (again....clean bottom....very important). That will give you optimum performance.
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