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Old 09-01-2013, 09:20   #1
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Skeg effect on prop efficiency

I am considering making an offer on a home built cold molded sailboat. Its an uncommon design Reliant 49. The one for sale has the skeg with the sides that protrude out at the sides before angling in to the prop area. The other photo is of another home built boat of the same design and the skeg is the same (narrower) width throughout. I don't know which was built to plan but do you think the wider skeg will dramatically affect the efficiency of the prop compared to the thinner profile version? Have you seen other skegs with a similar shape to the one in the first photo? The second photo may be of an unfinished skeg as I can't see the hull. Also the second photo has vertical metal plates embedded on both sides of the skeg and the bolts are buried in the raised horizontal sections. Perhaps the first photo builder simply closed in the whole area instead of having sections stick out.
Your collective wisdom would be appreciated!
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Old 09-01-2013, 09:24   #2
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Re: Skeg effect on prop efficiency

If I see how big the blind area before the prop on the firs picture and how close the prop is too it I would expect vibrations and efficiency loss from it. Most boats have a skeg that ends very sharp near the propeller to prevent turbulence and vibration. The second one looks more "normal"
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Old 09-01-2013, 11:10   #3
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Re: Skeg effect on prop efficiency

I may have more photos today of the boat for sale. This could explain why the owner thinks the cutlass bearing should be checked when the engine (and perhaps the boat itself) has only 181 hours on it. here are a couple more photos of the comparison boat skeg.
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Old 09-01-2013, 11:29   #4
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Re: Skeg effect on prop efficiency

Wow, that skeg (#1) looks real thick. I would think it would effect the prop alot.
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Old 09-01-2013, 11:50   #5
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Re: Skeg effect on prop efficiency

The prop shaft is 11/4" thick and I think the comparison boat skeg lumber is 2" thick. There must be some kind of bearing or bushing in the skeg for the shaft to go through. The boat for sale skeg seems seriously overbuilt and to the detriment of proper operation. I am trying to get an answer from the seller who is the original builder, or the surveyor.
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Old 09-01-2013, 12:36   #6
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Re: Skeg effect on prop efficiency

I too believe that propeller efficiency will be adversely affected by that design. IF you have doubts you might simply ask a Naval Architect for an opinion. If you had to pay him a few bucks for that service it could save you many more in the future!

Otherwise the construction looks good...

Cheers,

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Old 09-01-2013, 12:50   #7
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Re: Skeg effect on prop efficiency

Thanks, I emailed Glen-L, the firm who designed and still market the design to see if they would be able to tell me if it is a major issue.
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Old 09-01-2013, 14:45   #8
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Re: Skeg effect on prop efficiency

There will be some effect on motoring but as long as you use a 3 blade propeller you will be fine. Every full keel boat has the same issue. Remember that the compromise is that with an unprotected propeller, it is vulnerable to crab pots and other things such as line, parts of trees, etc. When the prop is protected like this one, you will lose a little efficiency but will gain a lot of safety.
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Old 09-01-2013, 14:47   #9
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Re: Skeg effect on prop efficiency

Well the surveyor weighed in and I quote, "The propeller has a 20" diameter, I find it hard to believe it doesn't get enough water, or that turning as slow as it does it might be cavitating"
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Old 09-01-2013, 15:05   #10
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Re: Skeg effect on prop efficiency

I would make sure you take it for a run before you make an offer. If they won't test sail it before offer then I would walk.

The effect of that large tree infront of you small propellor will be huge.

BTW you whose surveyor looked at it? You need independant guy.... But first and foremost realise that you ned to run it yourself before offer. They will try for a sail test after you have paid your 10%.

I think it's wrong. I would be ultra skeptical. I know how much I use my engine.

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Old 09-01-2013, 15:07   #11
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Re: Skeg effect on prop efficiency

It appears that measurement "C" may not be large enough. Hard to tell from picture.

Steve
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Old 09-01-2013, 15:26   #12
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Re: Skeg effect on prop efficiency

On our former sloop with cut-away-forefoot keel, we used a two-propeller blade which we lined up vertically directly behind the keel to reduce drag when sailing. Are the subject boats motorsailers?
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Old 09-01-2013, 15:39   #13
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Re: Skeg effect on prop efficiency

I agree it's difficult to tell from the photo angle. here is a different shot that makes it look better but that's because of the angle it was taken at...and one more.
Also I can't really take it on a sea trial as it is a project boat, though not in the usual sense. It was never really 100% finished. It was first launched in 2007 but I don't know that they ever even had the mainsail on. The two AGM 8D batteries are shot and its been on the hard for most of it's life. Also "cough" I'm in the middle of nowhere, Afghanistan right now. Don't yell at me, I'm very sensitive. I know what you are thinking and yes it's true...I am crazy. I like to break all of the unwritten rules at one time, sight unseen, custom, wood (cold molded), too big, not enough experience, not ready to work on it right away etc
here is the link to the Yachtworld ad
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Old 09-01-2013, 16:08   #14
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Re: Skeg effect on prop efficiency

I got one photo taken today that shows the prop from the other side and it doesn't have that same shape on that side at least from this angle. There may be more photos coming.
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Old 09-01-2013, 18:21   #15
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Re: Skeg effect on prop efficiency

Connie and I looked at this boat a while back. All we can say is she's bilt hell for stout!! she needed a little more work then what we wanted to do ! I see the price has dropped since we looked at her! I saw nothing with the prop set up that would be a problem ! If ya want a stout boat that needs some work to be ready and can get it for the right price, You would might wnt to give this boat a look see, or have someone ya trust look at it for ya ! for a younger fella that don't mind the work it would be a good one, if the price is right !! just our 2 cents
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