lcochrane
New member
Does anyone have thoughts on the pros and cons of lengthening a shallow draft cast iron bulb keel (4 foot 3") on a 34.2 ft Jeanneau.
Keel modification
- Thread starter lcochrane
- Start date
oldsaltoz
New member
There must be plenty of deep keelers looking for a shallow draft keel to access more areas that the deeper keel prevents them getting into.
Will you happy with fewer places to drop the pick? or lose the ability get a little closer to shore to get out of the swell or do a pick up/drop off?
Good luck and fair winds.
Will you happy with fewer places to drop the pick? or lose the ability get a little closer to shore to get out of the swell or do a pick up/drop off?
Good luck and fair winds.
fireball
New member
What are you trying to achieve - greater righting moment or less leeway? Or both?
davidej
Well-known member
How would you go about it?
Cut it in two horizontally above the bulb and weld in an extension?
I'm no expert but sounds a bit extreme to me.
Cut it in two horizontally above the bulb and weld in an extension?
I'm no expert but sounds a bit extreme to me.
RobinBirch
Active member
.....Ah yes your insurance proposal.....your reply to "has the vessel been modified in any way?"......
Sandy
Well-known member
I'd contact Jeanneau and discuss the project with them. See what the designers got to say on changing the shape of the boat.
Twister_Ken
Well-known member
Trouble is if you start messing with one parameter you change others. If you can deepen the keel but keep the weight, the centre of lateral resistance and the centre of gravity in the same place, you'll get away with it. If you end up with an increased righting moment you'll put increased strain on the standing rigging (she'll carry more sail in a given wind strength) and you might need to beef up shrouds, stays, chainplates and keel bolts. If you add weight, your power to weight ratio will suffer - she'll be slower, especially in light airs. If you move the CLR you might introduce hard-to-cure lee or weather helm. Not easy, and I'd consult an naval architect rather than the forum before starting work.
haydude
New member
A weld would rot in no time and eventually become a dangerous weak point. In such case one should use bolts and screws. But I would never even consider to modify a keel that way (classic that'll do!). A proper job would involve replacing the keel with one DESIGNED for the boat. But ... removing the existing keel, which is not only bolted, but also glued to the hull will do a lot of damage to the hull. THEREFORE:
The most cost effective way to replace a keel is to sell the boat and buy one with the keel you want.
Or just, forget it!
Tranona
Well-known member
I have been round this one with my shallow draft Bavaria 37. Everything is the same for the deeper draft - same rig, except for the keel and the rudder. The keel is actually heavier to give the same righting moment, but has a large bulb at the bottom. The loss is in performance to windward because of the shallow keel. One possibility is to drop the keel and insert a spacer, but you would end up with very long keel bolts - and still have the shallower rudder.
As already suggested, better to sell the boat and buy one with the deeper keel if you think you really need it. If not, enjoy the somewhat narrow benefits of the shoal draft. (We bought ours to transit the Canal du Midi).
As already suggested, better to sell the boat and buy one with the deeper keel if you think you really need it. If not, enjoy the somewhat narrow benefits of the shoal draft. (We bought ours to transit the Canal du Midi).
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William_H
Well-known member
I would say that Ken's comments might seem theoretically correct but not in practice. Most of the righting moment of your normal boat sailing at normal angles of heel comes from the hull shape and the total weight of the boat. Only beyond perhaps 45 degrees of heel does the weight down low of the keel start to produce real righting moments. So in practice no concern about rig strength unless you intend to lay it over on its beam ends. Hence many boats have much of the ballast under the floor boards rather than keel tip. Of course keel tip is better but not so much as you might imagine.
However the length of the keel might have a large effect on leeway and windward performance. Likewise a longer rudder will give better windward control and performance.
OP is probably just speculating but a deeper rudder might just give improvement at a much easier cost.
You can add a frangible extension using foam and f/g fairly easily. Frangible meaning it can be broken off in a grounding without damage to the original rudder.
A new cast keel or fit a correct deep keel might be the answer for the keel rather than extend it.
good luck olewill
Plevier
Active member
Rather an extreme example but you might like to look up the accident report on Hooligan. Consider the position that would put a manufacturer in too if you ask them to approve it.
C
catalac08
Guest
Cast iron is famously hard to weld and even if welded have you retained full structural strength? The last thing you want is your keel coming off because of a brittle weld and the very fact you ask the question suggest you are not an engineer. An alternative would be a shaped, machined billet bolted onto the bottom of the keel.
knuterikt
Active member
This boat was built with two different keel options, the shallow one being the heavy one..
maby
Well-known member
Indeed - I've heard of people changing the draft of a boat by replacing the keel with an alternative from the original manufacturer. I'm pretty sure there was a discussion thread on exactly this subject on the Jeanneau Owner's Forum.
It is going to be expensive - keels are ruddy heavy things, so you can't simply unbolt the old one, lift it away, lift in a new one and do up the bolts. We were considering buying a boat a year or so ago that had been grounded and had a leaking keel joint. I made enquiries with several boat yards about the cost of having it dropped and reseated - and they were all looking for between £1000 and £2000 just to do that. Add in the cost of the replacement keel - I can't imagine that Jeanneau would sell you one for less than £5000.
I suppose that you may be able to find someone with a deep draft version of the same boat who wanted to swap with you - but you would then be talking twice the cost of dropping and refitting.
knuterikt
Active member
My comment was targeted on those whining of Hooligan and other horror scenarios
Feasibility and cost is two different things.
I don't know about this boat, but often the short keels are made of lead.
Lot of the cost of a lead keel is the raw material, old lead keels can be sold at market value for lead or recast in a new form.
Dropping and attaching the keel is not that much work, cost can be cut if you are allowed to do some work your self.
There are some solutions to this that is feasible..
dulcibella
Active member
I'm not very happy with the idea of a spacer - won't this put a large bending moment on the keel bolts when heeled?
maby
Well-known member
It will increase the bending moment relative to that of the original shoal draft keel, but the result will be no more than it would for a purpose built keel of the same draft as the spacer plus original keel combination. However, I don't think that a spacer making any useful difference to the draft would be very practical. The OP is presumably thinking of adding a significant extra draft and to do this with a spacer would require some very long new keel bolts.
knuterikt
Active member
Isn't in a little bit strange that the OP is silent?
We really don't know his intentions.
But changing the keel from the shallow to the deep yard design wouldn't be risky..
If the existing keel is moved downwards with a "spacer" weight should be removed to keep the same righting moment.
To get at effective shape the keel might need to be "shaved" a little bit..
Here is the web site of a company i Denmark who make keels for a living.
http://www.oerkild.com/html/engelsk.html
Have a look at the bottom this page - there is an example of a spacer
http://www.oerkild.com/html/specialjobs.html
And here is a little bit on bolts also
http://www.oerkild.com/html/bolts.html
We really don't know his intentions.
But changing the keel from the shallow to the deep yard design wouldn't be risky..
If the existing keel is moved downwards with a "spacer" weight should be removed to keep the same righting moment.
To get at effective shape the keel might need to be "shaved" a little bit..
Here is the web site of a company i Denmark who make keels for a living.
http://www.oerkild.com/html/engelsk.html
Have a look at the bottom this page - there is an example of a spacer
http://www.oerkild.com/html/specialjobs.html
And here is a little bit on bolts also
http://www.oerkild.com/html/bolts.html
lcochrane
New member
Thanks for the replies
The main reason for considering the change was in the hope that a longer keel would make the boat stiffer as it heels a bit more in gusts than we like.
Also tends to swing around at anchor more than other vessels of similar size.
The main reason for considering the change was in the hope that a longer keel would make the boat stiffer as it heels a bit more in gusts than we like.
Also tends to swing around at anchor more than other vessels of similar size.
