Tranona
Well-known member
Not in modern construction where the bolts, or more usually studs do not get wet.
Fin keels - Moulded or attached fin?
- Thread starter doug748
- Start date
Not in modern construction where the bolts, or more usually studs do not get wet.
prv
Well-known member
You mean "should not get wet"
We've just had our keel dropped and re-bedded because water was leaking in between keel and hull and then up one of the keelbolts and into the boat.
Pete
doug748
Well-known member
Not at all.
Given two identical moderate cruising fin designs, I guess the hydrodynamic performance would be the same.
The encapsulated design would perform better on the water because it's Centre of Gravity is in the right shop. Too much of the cast keel is there simply to support the bottom third. The effect is made worse by all the frameworks and steel in the bottom of the boat designed to cope with point loadings and stop the thing falling off.
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prv
Well-known member
This all seems plausible, but the problem is that you simply can't build a modern keel shape as part of a GRP hull by any conventional method. (Or any unconventional method I can immediately think of, but there are some talented engineers out there).
Pete
TimBennet
New member
Moderate cruising fin designs with steel frame works? That's certainly not very usual.
Whatever aspect ratio you choose, a lead cast keel will always have a lower drag or lower Centre of Gravity than anything else bar none (legal). You can't wrap something of a given mass and density with a material that's essentially light weight (GRP) and not reduce these useful qualities.
The truth is, there are lots of good, reliable ways to construct a keel and many that are suspect. The distinguishing feature between them is certainly not whether they are encapsulated or not.
doug748
Well-known member
I should say there comes a point where an deep narrow keel cannot be supported by GRP alone.
Perhaps (leaving racing boats aside) this point may not be reached in the majority of curising designs? Or if it is, that the level of compromise in encapsulating a keel would not greatly affect performance.
Here is an Albin Ballad:
Cost is another matter
Perhaps (leaving racing boats aside) this point may not be reached in the majority of curising designs? Or if it is, that the level of compromise in encapsulating a keel would not greatly affect performance.
Here is an Albin Ballad:
Cost is another matter
doug748
Well-known member
"Moderate cruising fin designs with steel frame works? That's certainly not very usual." Tim Bennett
It is quite common though I agree not usual. That is why I was careful not to say it was.
It is quite common though I agree not usual. That is why I was careful not to say it was.
bbg
Active member
Fin is in.
Mould is old.
Mould is old.
TimBennet
New member
OK you say quite common. What percentage of moderate cruising fin designs are adulterated by steel frame works?
I wouldn't call X-Yachts moderate cruising fins and the other makes are ?
Neil_Y
Well-known member
I think you may be confusing racing with just modern cruising designs Doug, the Pogo 12.50 is a cruising boat not a race boat. Look at the designs from Rodger Martin for cruising boats, Cetacea (now an old design) was shallow long fin with wing.
If we go back a bit to the Twister, often seen as a traditional solid cruiser, it was designed to a racing rule of the time to give a good rating, it was a successful race design of the 60's.
So I don't think there is a particular link with keel type to boat use, just a gradual development of design.
Here's Cetacea keel (my personal favourite design for a cruising boat) based on BOC designs from the early 80's but built for circumnavigator who had been around once in an old long keel boat.
If we go back a bit to the Twister, often seen as a traditional solid cruiser, it was designed to a racing rule of the time to give a good rating, it was a successful race design of the 60's.
So I don't think there is a particular link with keel type to boat use, just a gradual development of design.
Here's Cetacea keel (my personal favourite design for a cruising boat) based on BOC designs from the early 80's but built for circumnavigator who had been around once in an old long keel boat.
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sailorman
Well-known member
have you seen the cost of a Pogo
doug748
Well-known member
A number of boats boast steel reinforcement in the hull. The rest all have studs and/or washers, spacers, backing pads and nuts to hold the thing together. What I said was:
"The effect is made worse by all the frameworks and steel in the bottom of the boat designed to cope with point loadings and stop the thing falling off. "
sailorman
Well-known member
Real boats dont have that steel grid. its all done to save weight & money
Resolution
Well-known member
I do look forward to the day when hydraulic-powered canting keels are to be found amongst regular cruising yachts. That would give you guys something to disagree over!
Neil_Y
Well-known member
TimBennet
New member
Well having done dozens and dozens of stability analyses of yachts, I can assure you your concerns are unfounded. Even the heftiest of nuts and washers would have zero effect as they will generally be about or even below the CoG.
If you're going to worry about anything, then you should be concerned when encapsulated ballast isn't a single block of lead (or less good cast iron) but is a series of ingots or even smaller pieces of ballast incorporated in putty placed in the fibreglass shell. I've seen examples of this where the entire ballast package (ballast material, putty, and encapsulating grp shell) has a significantly lower overall density.
Short of using spent uranium, there is no way of getting the lower extremity of a keel (the working bit) any denser, with more of it's material where it's needed, than with a cast lead appendage. However, if you have a long keel with sufficient room to pack the lower portion of the grp envelope with will shaped, tightly fitting lead blocks, then people may prefer the advantages of having no keel bolts over having the lowest CoG achievable.
geem
Well-known member
Short of using spent uranium, there is no way of getting the lower extremity of a keel (the working bit) any denser, with more of it's material where it's needed, than with a cast lead appendage. However, if you have a long keel with sufficient room to pack the lower portion of the grp envelope with will shaped, tightly fitting lead blocks, then people may prefer the advantages of having no keel bolts over having the lowest CoG achievable.[/QUOTE]
There is. Tungsten is 50% heavier than lead. It used for balance weights on F1 cars.
There is. Tungsten is 50% heavier than lead. It used for balance weights on F1 cars.
ganter
Member
Until you hit something and the encapsulation fails.
Bolt it on. Have access for maintenance.
Example 1)
How can you torque the bolts if they're laid up in GRP?
Example 2)
How do you drop the keels 3" every 3 years to renew sikoflex and retighten?
Example 3)
If you're trying to pull speed from the boat - you should have bought something faster in the first place.
TimBennet
New member
Cheapskate. Why not use gold or platinum.
Since the use of spent uranium by Eric Tarbaley's boat's keel (in the 70's), anything more dense than lead has been banned for racing. No cruising boats have wanted to pay for anything denser either.
Daydream believer
Well-known member
No body has mentioned it but I would have thought a strong design would be a fixed keel set into a deep socket in the hull & bolted as well
There are some like that
& of course lift keels are similar of sorts in the way the hull is used to brace the lateral forces
There are some like that
& of course lift keels are similar of sorts in the way the hull is used to brace the lateral forces