Folding up keel.

Discussion in 'Boat Design' started by BertKu, Jul 26, 2016.

1. Joined: May 2009
Posts: 2,310
Likes: 32, Points: 58, Legacy Rep: 223
Location: South Africa Little Brak River

BertKuSenior Member

Yes, I had already a gut feeling that I need high currents. The surface area is 4.4 meter = 44 dm x (50mm round)= 1,5 dm = 66 dm2 x 2 (inside also) = 132 dm2 x 0.15 Ampere = about 20 Ampere. I have a 12 Volt 1 KVA transformer which should do the job. Thanks for your great help.

Now,I still need somebody to tell me whether i should, for the 4.6 meter high mast, make stringers or to leave them out. Many thanks, if somebody can enlighten me. I have difficulty in calculating the forces, a 7 m2 sail and a 4.6 meter mast with a wind force of 7 m/per second. What forces will it have on the top of the 4.6 meter mast. (preferable in kgmeter) Then I could consider to place a stringer on the mast or not. Bert

Last edited: Dec 18, 2016
2. Joined: May 2009
Posts: 2,310
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Location: South Africa Little Brak River

BertKuSenior Member

Let me formulate my question in a simpler way. Is it correct what I have drawn on the attached drawing. Is it correct that if stringers are mounted the mast will bend less. Many thanks if somebody can confirm this.
Bert

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3. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

My apology, no wonder I could not find anything on the Internet. The name is spreaders and not stringers. In the meantime I found this on the use of spreaders and have decided to place them on the mast. If at 2/3 position it is wrong, please correct me if it should be otherwise.
Thanks IKE. Bert

"What is the purpose of spreaders.
They increase the angle between the mast and the shroud. This reduces the shroud tension and the compression force in the mast for the same sideways force when compared with a straight shroud. They also break up the length of the mast into a number of bays between points of restraint. This greatly increases the mast's resistance to buckling under compression load."

4. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

What the hick have I done wrong. I followed the advise and instructions from the Practical Boat Owner, page 66 and that of CDK and I have a beautiful anodised product. However some parts does still make low resistance while other parts are high resistance as it should. I have no hope to anodise my mast when those small jobs are not absolute perfect. They look beautiful, but I suspect that the shop who sold me the "pure" lead weights used by fishermen may have some contamination or the article stated max 23 degrees, while our ambient temperature is already 28 degrees, it is summer here. Or maybe I did something else wrong. All what I can do is to powder coat the mast now. Has any boat builder ever used powder coated aluminium mast, spars etc in their design? Bert

5. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

Sorry that it took a little while, but here is the not yet final welded folding up keel. I had some medical treatment. Before I am able to weld all parts permanently, I have a question on the position of the keel. I am planning to place the keel, about 10 % of waterline between mast and front of keel (drawing attached) the keel is turning around 2 points and has a spring in front (photo attached) , should I hit an object, the keel will not tear loose from the hull, but the boat will merely slow down fast (10 cm)
The keel will be pulled up by the 2 stainless steel wires and placed into position with a max 1000kg tape band. Yes, yes I will have a little drag, but it is not worrying me.

My question is >>>> Is 10% fine (45 cm) or should it be less, or more. Both which I prefer not, due to the positions of the trailer rollers on which the boat is pulled into place. Appreciate your views, Daiquiri, PAR or anybody who is more knowledgeable then me.

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6. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

Hi all,

Is there really nobody who can advice me whether 45 cm (approx 10% of waterline) between mast and folding up keel is fine or badly wrong. Bert

7. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

Well I had no response from the members, so I had to take a chance.
At last the folding up keel is mounted onto the boat and I must say, it does not look too bad. As soon I have the time I will test it with sailing with a sail.

Photo 1 shows the keel in sailing position.

Photo 2 shows you the keel folded up to the port side.

Photo 3 shows you the folded up keel to the star side.

Photo 4 shows you the mechanism in lifting the keel up, however as soon I have established that it is a workable success after having gone onto the water, I will make the drum bigger en make it from stainless steel 316. For the time being I will have to face the fact that it will rust. Also I like the tape to be wider.

Photo 5 shows you the keel folded between the boat and trailer gliders. I was very concerned that I had overlooked something and that it was a flop. But so far, it fits beautiful between the spaces from the boat and boat trailer; although I had to add from wood a 50 mm higher glider to compensate for the 50 mm higher centre part which rolls over the trailer rollers. Also I had to re-carpet the new wooden portion. I had a choice of lifting the gliders by 50 mm, but the length of the 2 legs clamped onto the trailer part would have become very unstable, thus I decided to heighten the gliders. (Photo-6) Now I have to replace my older sail for a larger new one.

I am totally confused about the wide differences between weight/square meter sail for the one or the other sailboat.

1) Wolfhound, 44000 kg ,218 m2 sail i.e. 210 kg per m2 sail

2) Legend 31, 5443 kg, 54 m2 sail i.e. 100 kg per m2 sail

3) UQ37 Eb en vloed, 16500 kg, 82,5 m2 sail i.e. 196.3 kg per m2 sail

4) X-Yacht-X4, 8850 kg, 97 m2 sail i.e. 91.2 kg per m2 sail

5) Maxi 1100 , 5800 kg, 70 m2 sail i.e. 82.5 kg per m2 sail

6) My own boat 750 kg, 8 m2, sail i.e. 93.7 kg per m2 sail

I would have thought that the m2 roughly would be the same for all yachts.

Bert

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8. Joined: May 2003
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Location: Sydney Australia

CT249Senior Member

There is no reason at all for the sail area to displacement ratio to be the same for all yachts. It varies according to many criteria - for example, how stable is the boat? What is it designed for? How expensive is the construction? What area is it designed to sail in?

Obviously a cheap, shallow boat built out of concrete for family cruising around Cape Horn is going to have a lower power to weight ratio than a billionaire's boat for racing with a pro crew on a Swiss lake, just as an old 4WD truck converted into an all-terrain motorhome is going to have a lower power to weight ratio than a F1 car.

9. Joined: May 2009
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Location: South Africa Little Brak River

BertKuSenior Member

Thank you CT249, I did it to see whether I was in the ball point figure or way out. It seems that PAR and others were right that with 7 to 10 m2 sail it should be fine.
Bert

Last edited: May 8, 2017
10. Joined: May 2009
Posts: 2,310
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Location: South Africa Little Brak River

BertKuSenior Member

My apology CDK, your suggestion of a two point swivel system has worked out well. The only thing I have added are two stainless steel 316 springs, which should buffer any accidental hit at the front or while reversing. Also I have made a contraption to lift and lower the keel. Thanks for your suggestion, hope you like that what I have created. Bert

11. Joined: Aug 2007
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CDKretired engineer

To me this all looks quite good. I hope you are going to be satisfied with how it performs at sea!

12. Joined: May 2009
Posts: 2,310
Likes: 32, Points: 58, Legacy Rep: 223
Location: South Africa Little Brak River

BertKuSenior Member

Thank you, I am first testing it out on the lake, the river is not deep enough when the tide is low. If it does not work, it is like playing golf. It hurts my pocket, but had the pleasure of playing. Here the same, if it does not work, I will take it off and use the metal for something else. Bert

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