Keels and Cores

[GrahamCownie]

Hi All,

I'm rapidly running out of reasons not to buy a yacht - apart from the obvious one that it makes no financial sense! I'm pretty much decided on an Elan Impression 434 - mostly for coastal work around the UK, but also for the occasional jaunt into deep blue Atlantic water. I have two questions sorta related to this yacht.

Firstly, it seems that one of the main reasons why people wouldn't consider the Elan to be a "true" bluewater yachts is the fin keel. If I have it right the issue seems to be that a fin keel is susceptible to damage (underwater containers etc). It presumably isn't solely related to the fact that the keels are bolted on (Hallberg Rassys have bolt-on keels) so presumably the thing that makes the HRs safer is their "long" keel with swept leading edge? (Oh and the skeg rudder). In which case why is it so difficult for a designer to create a swept leading edge to a fin keel to mitigate the forces of impact?

Second question. A Jordan series drogue seems like me to be a no-brainer, must-have bit of kit. The great man himself recommends chain plates at the aft end of the hull to take the loads. Is this feasible or practical on a yacht which has a cored hull? Is there enough stength in a sandwich construction hull to take the loads imposed by a series drogue? Will putting bolts through a sandwich construction hull compromise the integrity of the core?

Many thanks in anticipation,

Graham

[sailingdog]

Graham-

Generally, creating a long swept leading edge to a fin keel is going to add a good deal of wetted surface area. As such, it will be detrimental to the performance of a higher performance sailboat, for very little return in most cases. They could do it...but it would make their designs slower.

Yes, you can add such chainplates to a cored hull. You might want to talk to a marine architect about the best way to do this. Ideally, the chainplates would be installed in such a way that they spread the load over a good section of the hull and deck, so that they don't strain any one point too much.

[GrahamCownie]

Thanks Sailingdog. I certainly wouldn't do chainplate work myself. Definitely one for the engineers - but good to know that it can be done.

[JohnRPollard]

Originally Posted by GrahamCownie

Firstly, it seems that one of the main reasons why people wouldn't consider the Elan to be a "true" bluewater yachts is the fin keel. If I have it right the issue seems to be that a fin keel is susceptible to damage (underwater containers etc). It presumably isn't solely related to the fact that the keels are bolted on (Hallberg Rassys have bolt-on keels) so presumably the thing that makes the HRs safer is their "long" keel with swept leading edge? (Oh and the skeg rudder). In which case why is it so difficult for a designer to create a swept leading edge to a fin keel to mitigate the forces of impact?

Graham,

I'm a bit puzzled by your impression that a "fin keel" is considered more susceptible to damage than a full keel. I would argue that in some cases, the opposite could be true. Your question about swept leading edges is curious as well.

To the best of my knowledge, the vast majority of modern bluewater boats have fin keels with swept leading edges. Most of these keels are bolted and bonded to a keelson stub, although there are still a few brands out there that have internal ballast encapsulated in fibreglass. The leading edge is swept aft -- with a modest performance penalty -- for the simple reason that the sweep allows the keel to shed kelp, weed, grass, lines, and other floating debris. It is common practice. There may be a slight advantage in a hard impact, but that's not the primary reason for the sweep.

Usually the discussion concerning "susceptibility to damage", in the context of fin keel designs, focusses on the rudder -- particularly what we refer to as unprotected spade rudders. Many, but not nearly all, off-shore cruisers are somewhat uncomfortable with this rudder arrangement. However, there seem to be very few sailors left that insist on a full keel to protect their rudder -- most are quite comfortable with a fin keel and a sturdy skeg-hung rudder.

"Fin keels" can come in many shapes and sizes. As mentioned, cruisers usually prefer a swept leading edge, but they also tend to prefer a moderate draft and a fairly large footprint where the keel attaches to the hull. This usually translates into a longer fin, what is often referred to as a "cruising fin", a la HR, Pacific Seacraft, etc, frequently followed by a skeg-hung rudder.

I took a look at the Elan website but the only underwater view I was able to quickly find was this one: ELAN Marine - Sail - Sail Yachts
I have no firsthand knowledge about this boat brand, but assuming it is well designed, engineered, and constructed, there isn't anything inherently wrong with the 434s keel arrangement. However, it certainly does have a nearly vertical leading edge -- good for performance, not so practical for shedding debris. I couldn't see the rudder, which is another aspect of the design that deserves focus.

[sailingdog]

JRP-

The angle the keel's leading edge is at on most fin keels is far more vertical than that of an older full keel design.

If you look at the angle of the forward edge of the keel on this Alberg 30, and compare it to the image in your signature, you'll see what I mean.

[JohnRPollard]

Originally Posted by sailingdog

JRP-

The angle the keel's leading edge is at on most fin keels is far more vertical than that of an older full keel design.

If you look at the angle of the forward edge of the keel on this Alberg 30, and compare it to the image in your signature, you'll see what I mean.

Sure, I won't argue with that. But I think the primary reason you see more rake in the full-keelers is because the full-keeler (even those with a cut-away forefoot) has plenty of chord for lift, so they do not have to worry about sacrificing area with a long rake. With a fin keel, there is only so much of the keel area that can be given over to rake on the leading edge (without sacrificing chord length or unduly increasing wetted surface), so a compromise must be struck.

Obviously the more rake, the better the keel will shed floating debris. But I seem to recall the compromise number used on many fin-keel cruising designs is in the neighborhood of 42 degrees of sweep/rake -- this amount having been found adequate to shed kelp and nets. Incidentally, that same amount needs to be carried over to the leading edge of the skeg as well, in order to get the benefit.

I think we're getting into a difference on semantics -- I guess compared to your example my boat (in my signature) doesn't have a lot of rake. But I would argue that there is quite a bit of rake/sweep in the fin-keel design on my boat. Sure, not as much as that Alberg 30, but FAR more than the nearly vertical leading edge of the Elan. On the other hand, a Cape Fear 38 owner might view the Elan keel as very "cruisey."

[camaraderie]

I don't have any problem with fin keels on cruising boats. While the Elans is classified by them as a bulb keel, it is rather more like a wing or schell fin keel in its' execution which is much better supported than a bulb for cruising needs. I would be much more concerned about the spade rudder for cruising purposes but obviously many others go cruising with spades...I much prefer the protection and support of a rudder skeg.
I also don't like saildrives for cruising as maintenance and repair is difficult in 2nd and 3rd world venues and over the years it seems like saildrives have had quite a lot of problems. Just look at the recent issues with Tartan/Yanmr saildrives, Giuliettas replacement and the notorious OMC drives. Yanmr has been excellent about standing behind their product but I wouldn't have one unless I needed an extra 1/2 knot in the local race scene.
That said...I really like the way the boat is put together and it should be a joy to sail and quite quick. The layout and tankage and interior spaces seem to be well thought out for full time cruising and it is a distinct departure from the Elan's I have been familiar with. It is an excellent value and with a few upgrades I think this boat would make a fine cruiser and you might want to consider asking the factory to incorporate them during the build process as they seem like they are amenable to minor changes unlike many production mfrs.
1. Provision for dual anchor rollers and windlass and chain/rope storage that can handle dual rodes.
2. Large house bank of batteries (AGM's for full time cruising would be my choice.) Upgraded charging alternator and 3 step regulator.
3. Alternative charging system...generator/hi-amp charger or passive system (wind-solar)
4. Stern strong points for drougue.
5. Life raft cannister on deck.
6. Stowable emergency rudder.
7. Additional hi capacity electric and manual bilge pumps.

Hope this is helpful for you. Good luck with the decision making.

[seabreeze_97]

At a glance it would appear the 434's capsize ratio may be what is considered poor for bluewater activities. Nevermind the fin.

[Gramp34]

Originally Posted by GrahamCownie

Second question. A Jordan series drogue seems like me to be a no-brainer, must-have bit of kit. The great man himself recommends chain plates at the aft end of the hull to take the loads. Is this feasible or practical on a yacht which has a cored hull? Is there enough stength in a sandwich construction hull to take the loads imposed by a series drogue? Will putting bolts through a sandwich construction hull compromise the integrity of the core?

I think it's wise to raise this question. The aft chainplates are designed to carry a primarily vertical load while the drogue will be a horizontal load. In older, heavily built solid fiberglass hulls there would be plenty of strength, but in modern highly engineered weight optimized cored hulls, the chainplates may not be able to carry this load they weren't designed for.

The sheet winches are plenty strong. What about making a bridle for the end of your drogue that has spliced eyes to go over the winch drums? Easy to set, strong and won't require engineering and fabricating special attachment points.

Cheers,

Tim

[sailingdog]

Gramp

Jordan recommends installing new, separate chainplates specifically for the jordan series drogue bridle. He doesn't suggest that you use the backstay chainplates. Most backstay chainplates are inboard. The JSD chainplates should be as far outboard as possible.

Originally Posted by Gramp34

I think it's wise to raise this question. The aft chainplates are designed to carry a primarily vertical load while the drogue will be a horizontal load. In older, heavily built solid fiberglass hulls there would be plenty of strength, but in modern highly engineered weight optimized cored hulls, the chainplates may not be able to carry this load they weren't designed for.

The sheet winches are plenty strong. What about making a bridle for the end of your drogue that has spliced eyes to go over the winch drums? Easy to set, strong and won't require engineering and fabricating special attachment points.

Cheers,

Tim