Elan 36 short vs deep keel

[knuterikt]

I have found a used Elan 36 that I like.
Only one thing worries me, this boat is a short keel version.

I have found out that this boat come with two keel versions. One deep (1,95 m / 2200 kg) and one short (1,40 m / 2500 kg). Someone told me that the version with short keel was more course unstable than the long keel version.
Do you have any comments to this?

TIA
Knut

[SeaSpark]

If possible try find a deep keel version.

The only real benefit of the shallow keel is it extends your cruising possibilities in shallow water. For cruising the Dutch inland waterways for example this is important not so for the Norwegian coast i guess.

The major benefit of the deeper keel is much better upwind performance (tacking up a fjord?).

Jeroen

[knuterikt]

Do you know to what degree the shallow keel alternative will degrade performance upwind for this boat?

tia
Knut

[SeaSpark]

You could ask Elan for a polar diagram from the two different versions. They have a detailed one for the 37 http://www.elan-marine.com/marine/ra...an%2037-GZ.jpg so perhaps they can dig up one for 36 versions also.

[kenJ]

The fin keel (long) will point higher than the shoal draft. From experience in a similiar production boat, for cruisers it will be transparent, sail trim/sail condition/rig tension has more effect. If racing is the reason for the purchase and the water depths aren't a problem then a fin is better.

[SuperPiper]

I'm thinking that both configurations provide the same righting moment: 2200kg @ 1.95m or 2500kg @ 1.40m. The obvious benefit of the deep keel is that the boat weighs 300kg less (and may be a few dollars cheaper). Provided that the proportions of each keel creates the same amount of lateral area, should you really expect a difference in performance?

[JesperW]

The righting moment is equal to weight times righting arm, not weight times draft.

Increasing the draft some distance will only increase the righting arm about half that distance, if the keel geometry is kept constant. Unless the shallow keel has a much larger bulb than the deep (which will move the center of gravity downward), it will propably have less RM.

Also the shallow keel has a lower aspect ratio, which means that even if it has the same lateral area as the deeper, it will be less effective.

But still, as said before, you are only likely to notice the difference if all other performance aspects are well trimmed, such as when racing.
/j

[kenJ]

JesperW
Most shoal draft keels weigh more than the fins to keep the RM about equal. They do this usually by adding thick "wings" to the bottom of the keel. Some designers do use bulbs, usually those in the racer class rather than strictly cruising.
I thought the higher pointing of the fin keel came from a better/longer foil shape producing more lift to windward, rather than just reducing heel, which I think is what you are referring to in the aspect ratio comment.

[JesperW]

Originally Posted by kenJ

I thought the higher pointing of the fin keel came from a better/longer foil shape producing more lift to windward, rather than just reducing heel, which I think is what you are referring to in the aspect ratio comment.

Yes exactly. For example, with everything else the same, a keel with Aspect Ratio = 3 should need less than half the leeway angle of a AR=1 keel to produce the same lift force. And it will have less drag.

The difference between the AR of the Elan keels in the original post is much smaller, of course.