Keel taper question

[bruce d]

Hello, I am looking for some help. It concerns the keel of a Bermuda built schooner circa 1800.

The keel is 10 inches breadth tapering to seven inches at each end. The question is: where does the taper commence?

 

The options seem to be …

(1) There is a section in the middle of the keel where the sides are parallel and then the taper begins at a point approaching each end. If so, where does the taper begin?

(2) The keel has little or no parallel section with the tapers starting from (presumably?) the width extreme point. It would be very easy reading various scantlings to believe this was the intention. This option seems pointless but what do I know?

 

Thanks in advance,

Bruce

[Mark P]

Good Afternoon Bruce;

 

This is a much-debated point. I did once see an explanation of where the taper began, but I cannot for the life of me remember where it was. 

 

However, to answer your question, but only in respect of the Royal Navy methods (however, merchant builders would almost certainly have followed a technique which allowed them to use thinner timbers at any part of a build, thereby saving money) the central section was parallel-sided. This extended some distance fore and aft, and seems to have taken up approximately half the keel length. However, that does not mean that a quarter of the length each end was tapered. As the keel at the bow was much less tapered than the stern, the length of the stern taper is much longer than the bow. if you split the remaining half of the keel into thirds, and allow two thirds at the stern, and one third at the bows, you will be about right. 

 

Another point is that the taper is not constant (judging from the body lines on draughts) but becomes sharper towards the extremities; so that the narrowing is actually slightly curved. 

 

I would be happy, though, to hear from other members who know anything more precise. 

 

All the best,

 

Mark 

[Jaager]

If the rule for this is not set in the texts that we have, it was likely a situation with fairly loose limits.

For warships, I would take the start of the deadwood as being where I could start a tapper.

The ASA 1870 allows that frames can be farther apart and the space 10% wider for the final 1/5 at either end. This may be a clue as to how the strength requirements for a hull were viewed.   The internal rise of the frames do not allow for as much cargo weight at the final 1/5, fore or aft, so the keel may have been allowed less mass starting there.  The lengths of the keel pieces and the length of the scarphs may hold a clue.  Begin a tapper - after the scarph of the last piece at either end.

 

Unless rich and building an America's Cup racer, I could not imagine expending money on the additional labor cost that a continuous taper would require. It would far exceed any savings on lumber for the keel.

[bruce d]

2 hours ago, Mark P said:

This is a much-debated point. I did once see an explanation of where the taper began, but I cannot for the life of me remember where it was. 

Me neither! I know it exists because I scribbled in a margin on a drawing 'taper: see discussion'. The explanation you

gave tallies with my recollection, many thanks.

 

1 hour ago, Jaager said:

Unless rich and building an America's Cup racer, I could not imagine expending money on the additional labor cost that a continuous taper would require. It would far exceed any savings on lumber for the keel.

Since this much too early for such sport I expect there was another practical reason for a tapered keel. The only guess I am willing to put forward is the belief that maximum strength was needed in the middle of the hull structure and the taper was seen as part of the process of fairing in all underwater lines. Stem and sternposts did not need to be as wide as the widest part of the keel but the keel needed to be one continuous piece (thanks to scarphs) so they were used as the reference points for the fairing.

Maybe one day one of us will find 'the discussion'. but for the moment I believe I have seen enough to carry on.

Don't want to shock anyone but I may be starting a build log soon ....

Thank you both,

Bruce

[Mark P]

To respond to Jaager's comment re the additional cost of labour to provide a taper, I don't think that this would be a consideration.

 

The essential point is that a tapering keel can be obtained from less costly, smaller sections of rough timber. The actual creation of the taper would be done when the timber was sawn. Many of a ship's timbers were sawn to both the sided and moulded dimensions, as it was much quicker than dubbing. A gentle taper would be no problem for skilled sawyers.

 

All the best,

 

Mark P

 

 

[bruce d]

Apropos to nothing at all, the keels of Bermuda built craft at that time were usually Honduran mahogany.

[mgdawson]

Hi Bruce,

I found a few threads by searching for "keel taper", include the quotes, that forces the search engine to look for the phrase rather than the 2 individual words that happen to be in the same post but unconnected.

Mark

[bruce d]

14 hours ago, mgdawson said:

I found a few threads by searching for "keel taper", include the quotes,

Well, I should have known that trick but DOHH! it makes a difference. Thanks.

The subject clearly has demanded the best forensic approaches by some very experienced members. For example, from about post#197 in this thread...

... some clear light is cast on the subject and I have looked at the source documents cited. Yet, the source is describing practice in English shipyards and is biased on larger ships. The rule(s) related there are difficult for me to imagine were appropriate for a schooner, but I am not able to point to an alternative rule. However, the guidelines for keel taper explained by Mark in post#2 in this thread make sense and  seem to be reflected in a drawing I have seen of a late 19th century Bermuda built yacht.

Thanks for the input, I appreciate the help.

[Matrim]

(the post numbers by the way are at the top right of the post in format #9  - that post is on page 7 on my browser.

 

It basically shows how many very strong plans designers are on the site and are willing to discuss and assist. One of the strengths of NMM and we are lucky to have them all (I dont want to imagine how wrong my plans would be without their assistance..) . Plus it reminds me how fun drawing ship plans can be. You can such a sense of progress..

[bruce d]

This looks like a pretty clear statement on the subject:

 

... from page 179 of Naval Architecture: A Treatise on Laying Off and Building Wood, Iron, and Composite Ships (1876)

by Samuel James Pope Thearle

Naval Architecture- A Treatise on Laying Off and Building Wood, Iron, and Composite Ships 1876.pdf

Writing in 1876 his wording indicates he is describing an outdated practice but does not nail down when it was in use.