Swing keel flap question

[DennisRB]

I am currently restoring a 8M trailer sailor and there is a flap that covers the swing keel opening under the boat. This flap has had it. It looks like some sort of thick convas that is screwed down by brass strips either side of the keel slot opening.

What does this flap do? I am guessing reduces drag?

Should a just leave it off? As I am sure it produces more drag in the state it is in.

Should I replace it? I don't know how to go about replacing it though as I don't know where to get the material from. Does any one have any ideas on what I could use, or any other suggestions?

Thanks heaps :)

Boat is a Hi-way. Damn that 480KG keel was a prick to get out in my drive way :eek:

(I also wrongly posted this in the design forum, I tried to delete it but could not find a delete option, so feel free to remove it mods)

[mighetto]

There has been some experience on downwind points of sail suggesting that the dagger style centerboard is faster down wind if fitted with carpet and foam wedges so that the board slot can be free from turbulence when the board is retracted.

This has been observed on Snipes and is documented in Royce Sailing Illustrated.

I am unaware of swing style keels being fitted with carpet or foam wedges because these keels are not removed, as a dagger style foil is, on downwind points of sail. Instead they are swung back into the centerboard slot which blocks the slot and hence eliminates the potential of much turbulance. There is very little difference between a dagger and a swing centerboard on a boat that is balanced perfectly. In fact there may be none.

However the prior owner of your vessel must have found it of value and this was likely because he or she was prevented by racing or rating rules from retracting the centerboard at all. Such rules are giving way quickly. The manufacturer likely intended you to retract the foil on downwind points of sail and the flap likely does nothing for performance. But run some experiments. I would be very interested in seeing data on this.

[Paul B]

You might try this:

http://www.apsltd.com/Tree/d3000/e691.asp

I'm sure that performance sailing shops in most markets will have something similar.

[DennisRB]

Thanks Heaps guys. The boat is heavy and slow as it is and it to be used for cruising only as it is lucky to break 5-6K and tops out at about 8-9K under optimal conditions (gale force downwind leg) That said, I still want extract the best performance possible. The boat has been with my family for 22 years and was previously owned by the commodore of the Manly yacht club and was used successfully for racing. (back then it was considered a fast boat) So I guess the flap was there for a reason.

The keel is about 2000 X 500mm so when it is down there is a 1500mm opening that is about 100mm wide. Do you think this would add any meaningful drag? We normally wind it down a few turns on downwind legs just to give a bit of grip. Even when wound all the way up I would imagine the keel would not do such a good job of smoothening up the slot as it has a sort of knife edge, and would not fill a square hole real well.

I'm just not sure if I should bother as its just another thing that needs to be done right. And if done wrong might just increase drag. I would have thought that when the keel is down, it would open the flap up behind the keel and the flap would stick up increasing drag?

Do you think I should bother with it for this cruiser?

[mojounwin]

Hi Dennis,
My thoughts are that the flap is to cover the void left by the keel when down. Theoretically it should cut down some of the drag caused by water sloshing up inside the case. Practically I'm not sure there is any noticable difference, especially for a cruiser.

What sort of boat is she?

Also I see your from Brissy, here is an Australian Trailer Sailer Forum you might find useful if you haven't found it already.

http://groups.msn.com/trailersailerplace

Mike

[DennisRB]

Thanks

Its a Hi way (highway?) Shes about 8M long. Hi way 25? or Hi way 26?

Not sure about these boats, do you know anything about the make? I can't find any info on the net. I have seen a few around though.

[mojounwin]

Nah Dennis,
Haven't heard of them before.
If you ask on the Trailer sailer Place forum someone might know of them.

Do you have any photos?

Mike

[DennisRB]

Cheers. I joined and posted in that forum.

Traler sailer place (http://groups.msn.com/trailersailerplace/traileryachts.msnw?action=get_message&mview=0&ID_Message=17913&LastModified=4675532503030142788&all_topics=0)

[PAR]

The board slot flap can reduce turbulence a bit, but it's likely your boat will not be able to take advantage of the small percentage of a knot it may provide. On light weight racing craft, where any reduction in resistance can benefit boat speed, then this idea (flap) can be used to good effect. Your boat is a heavy cruiser and you wouldn't notice if it was there or not. It may also be used on your boat to help eliminate noise in the case area, which is another common reason for it's use. I have an early 70's trailer sailor of similar size, but it's shaped to be very stable and never plane, in fact advertised as unsinkable (lots of foam) It has two rubber (sort of long windshield wiper kind of things) let into small rabbets on the centerboard slot. They were pretty rotten when I got the boat so I removed them. The boat would make a lot of noise on certain points of sail with the board down. The sound was the turbulence in the slot. I replaced the rubbers and the noise all but disappeared.

[DennisRB]

This trailer sailer can plane given a strong enough wind from behind. I don't want any noise. So I think I will use "Slot Strip - Centerboard Gasket Material" Paul B linked to.

Does anyone know where I can get this in Australia?

[DennisRB]

Mike, I don't have any pics on digital. I can take some but they won't be very good as the boat will be in the same position as it is here. I have heaps of normal pics taken before the digital revolution but I have not scanned them.

Yes the boat is in this pic.... look closer! Its the only thing I have ATM. I will try to get some pics of the work progress on the weekend.

[DennisRB]

Here is a pic of the keel slot.

I posted some more pics of the boat and keel slot over here click me (http://www.boatdesign.net/forums/showthread.php?p=55104#post55104)

[WildCherry]

Its called a gasket. you can get one made to fit at a sail loft. use dacron material. It keeps water from coming into the area when the board is down. You will get a speed increase if you have it. but looking at your boat. who knows what speed you will get. It will help. but not much. good luck with it.

[DennisRB]

but looking at your boat. who knows what speed you will get

Thanks man :(

Its all I got and its over 30 years old.

[K4s]

We used to use two strips of thin but stiff mylar.One down either side of the case and overlapping down the middle of the case.Weather it helped speed wise who noes but it sure helped to make the boat quieter both sailing and anchored.