liam.mccaffrey
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| posted on 22/9/09 at 08:40 AM |
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Boat Keel Question
I have a friend who is into sailing in a big way and to increase the stability of his boat want to change the keel to a different design, one with a
larger area. He is very worried about the increased forces in the mast wires.
Does anyone know anything about this or could recommend a good source?
Cheers
Liam Mc
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Mr Whippy
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| posted on 22/9/09 at 08:44 AM |
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If it’s not a home made boat, I’d have assumed that the original designer had made the keel to suit the strength of the sail and mast. Tbh I’d rather
have a keel snap than rigging explode. Real question is…can he sail properly?
Fame is when your old car is plastered all over the internet
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alistairolsen
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| posted on 22/9/09 at 08:54 AM |
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quote:
Originally posted by Mr Whippy
If it’s not a home made boat, I’d have assumed that the original designer had made the keel to suit the strength of the sail and mast. Tbh I’d rather
have a keel snap than rigging explode. Real question is…can he sail properly?
if it s a yacht as opposed to a dinghy then a keel failure will result in a dangerous and permanent inversion followed in general by sinking so i
would far rather suffer a rigging failure.
Consider that most racing yachts are sailed with all of the crews weight adding to the effect of the keel and suffer no ill effects.
also depends on the age of the rigging, I would change it ever 5 years if racing, but a lot of boats are running 20 year old wire 
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MakeEverything
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| posted on 22/9/09 at 09:01 AM |
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quote:
Originally posted by alistairolsen
quote:
Originally posted by Mr Whippy
If it’s not a home made boat, I’d have assumed that the original designer had made the keel to suit the strength of the sail and mast. Tbh I’d rather
have a keel snap than rigging explode. Real question is…can he sail properly?
if it s a yacht as opposed to a dinghy then a keel failure will result in a dangerous and permanent inversion followed in general by sinking so i
would far rather suffer a rigging failure.
Consider that most racing yachts are sailed with all of the crews weight adding to the effect of the keel and suffer no ill effects.
also depends on the age of the rigging, I would change it ever 5 years if racing, but a lot of boats are running 20 year old wire
^^ What he said. The manufacturer would have designed the keep to be optimal, and having this 'snap' will pull the bottom of the boat out.
It may even be connected to the mast, depending on what boat it is.
Normally, if someone is in to sailing in a big way, they will buy a race yacht.
I wouldnt change the keel. There are other ways of getting more efficiency / speed.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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oldtimer
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| posted on 22/9/09 at 09:05 AM |
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This sounds very complex. The design of hull, keel, and rigging is usually co dependant. By increasing the area of the keel, do you mean as in long
keel (an alarmingly complex alteration) or deeper (which will have huge effects on the hull, rigging, mast load, etc) Getting a different boat souds
the most logical route.
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Mr Whippy
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| posted on 22/9/09 at 09:18 AM |
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The sailing dingy I have snapped its keel due to the previous owner having too much sail up, the boat simply capsized and he made a new one.
Considering the forces on the rigging wires and their usual fittings on the end of them, wires wiping around your face seems very dangerous.
Personally I don't think he should change a thing and if he's out grown the capabilities of the boat, it probably now time to move onto a
faster one.
Fame is when your old car is plastered all over the internet
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alistairolsen
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| posted on 22/9/09 at 09:27 AM |
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on the flip side, if its a cruising yacht that he sails shorthanded with reduced sail and just wants a little more stability then adding to the keel
is most likely fine.
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Peteff
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| posted on 22/9/09 at 09:41 AM |
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Is this like one of those "I have a friend with an embarrassing problem" questions you see in the magazines and you know it's really
the writer ? It's alright to admit you like boats Liam, no need to be covert. I will take this opportunity to admit that I quite fancy a go at
kayaking. 
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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liam.mccaffrey
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| posted on 22/9/09 at 09:50 AM |
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lol, no its not my boat though I have seen it. I do like to go out in my kayak though
quote:
Originally posted by Peteff
Is this like one of those "I have a friend with an embarrassing problem" questions you see in the magazines and you know it's really
the writer ? It's alright to admit you like boats Liam, no need to be covert. I will take this opportunity to admit that I quite fancy a go at
kayaking.
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Mr Whippy
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| posted on 22/9/09 at 09:58 AM |
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so then what kind of boat is it?
don't say a sailing boat 
Fame is when your old car is plastered all over the internet
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plentywahalla
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| posted on 22/9/09 at 12:55 PM |
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I don't understand why he wants to increase the area if he wants to make the boat stiffer. To do that he wants to add ballast to increase the
righting moment, not lateral keel area. that will, if anything will make the boat more tender as it will make less leeway.
This can be done easily by adding lead ballast inside the hull around the keel without adding stress loading on the keel bolts and floors.
Alternatively cast or bolt lead bulbs to the keel
The rigging wire spec is dependant on the righting moment of the boat which is a factor of both form stability (shape of the hull) and the keel. As a
general rule adding ballast of up to 30% of the keel weight is permissable without upgrading the rig spec as it would only add about 20% to the rig
loading which would have been designed with a 100% safety factor.
It would be useful to know the type of boat as race boats are built with much lower safety factors.
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CurlyBen
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| posted on 22/9/09 at 09:03 PM |
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Hi, I'm a bit of a lurker but this topic caught my attention - I know two people who were onboard a yacht which lost its keel and one guy died.
The failure was due to a few factors, including poor design, added weight and the keel manufacturer changing the design (they put a weld at the point
of highest bending moment to simplify manufacture) link. However, if it's simply a case of
worrying about the rigging, wire rigging gauges are not exceptionally expensive and will give a good indication as to the tension in the wires.
[Edited on 22/9/09 by CurlyBen]
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Ian D
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| posted on 22/9/09 at 09:23 PM |
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Look what happended to Tony Bullimor. He added weight at the bottom and reshaped his keel.
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Ian D
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| posted on 22/9/09 at 09:23 PM |
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Look what happended to Tony Bullimor. He added weight at the bottom and reshaped his keel.
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plentywahalla
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| posted on 23/9/09 at 10:15 AM |
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Both those examples were race boats which are notoriously designed on the limits or beyond in the name of performance.
It is highly dependant on the type of boat as to whether adding ballast is possible. Most GRP boats up to the '70's were massively
overbuilt. Early knowledge of the properties GRP was very limited and the assumption was that if a 28ft boat needed 1" planking when built in
timber, then it had to have 1" thick lay-up in GRP. So the were built like brick s**thouses (unfortunately they often sailed like one as
well)
If your friend has one of those then he could hang whatever he liked on the bottom.
On the otherhand anything built in France by the volume builders (Beneteau, Jeanneau, Dufour etc.) up to the '90's are very fragile. They
had some very odd ideas about how to stick the keel on and frequently they need strengthening just as they are.
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