Advice needed at final stages of lofting

[longfellow]

All long lines and body plans are faired in. I need to expand the transom but I have less than perfect information to do so. I gave preference to diagonals in getting a fair hull and if a WL or BL was out by an eighth or even a quarter, I left it. Please don't bash my technique here but I give preference to diagonals. If they are fair I believe that I will have a fine looking hull (especially if more diagonals than typical are given and I have five good ones on this hull. They, by themselves give a very complete picture of the hull shape). (My philosophy is...) that these are most representative of true shape since they are more "square" to the hull for more of their length and this is actually how you see the hull when you look at it. Bottom line is that now, since the WL and BL curves are exclusively used to expand the aft and fwd faces, and these lines on my lofting are out here and there by small amounts (18 foot daysailer), they are not going to give me an absolutely perfect expansion. My one thought here, if no one has any other ideas; since the last station is precisely AT the intersection of the rabbet line and the aft face (which means that I wouldn't have a mold here since it occupies the same space as the transom and transom frame), make the slightly angled transom plumb and I am not only done but I have a VERY accurate aft face expansion. It would actually be the body plan for this station. I know its cheesy but it will even help if I want to hang a small outboard. So it's a 17'8" boat now? Any ideas? Stations are 19.5 inches apart. Transom is angled about ten degrees. Ed

[TeddyDiver]

Sounds ok.. and I agree about the diagonals..

[Landlubber]

longfellow,

Do not loose too much sleep mate about lines lofted not being lines produced in actual fact.

1/8" is NOTHING........just remember to fair the framing as much as possible (with ply battens if you like), before plating. Any little errors can be shaved off, or added to to make the boat fair, this is the most important thing, getting it fair...bugger the measurements, that is for techno freaks that use computers to "build" anything, in real life there is no such thing as a true dimensioned boat (OK shoot me down now, there are a few so called perfect boats), just do your best not to have lumps.

Make the boat as designed, why alter the transom angle. The real life transom IS the last mold......

[rwatson]

Land L has hit the nail on the head - hell, with modern composites you can make inches of mistakes and still not compromise the strength of the boat.

if it looks fair, it is fair - its only the ego of the owner that insists on the mythical "perfect" boat.


"We do not know, what we do not know!" ??????

Heck - I dont even know what I DO know!!!!

[Guest62110524]

Originally Posted by longfellow

All long lines and body plans are faired in. I need to expand the transom but I have less than perfect information to do so. I gave preference to diagonals in getting a fair hull and if a WL or BL was out by an eighth or even a quarter, I left it. Please don't bash my technique here but I give preference to diagonals. If they are fair I believe that I will have a fine looking hull (especially if more diagonals than typical are given and I have five good ones on this hull. They, by themselves give a very complete picture of the hull shape). (My philosophy is...) that these are most representative of true shape since they are more "square" to the hull for more of their length and this is actually how you see the hull when you look at it. Bottom line is that now, since the WL and BL curves are exclusively used to expand the aft and fwd faces, and these lines on my lofting are out here and there by small amounts (18 foot daysailer), they are not going to give me an absolutely perfect expansion. My one thought here, if no one has any other ideas; since the last station is precisely AT the intersection of the rabbet line and the aft face (which means that I wouldn't have a mold here since it occupies the same space as the transom and transom frame), make the slightly angled transom plumb and I am not only done but I have a VERY accurate aft face expansion. It would actually be the body plan for this station. I know its cheesy but it will even help if I want to hang a small outboard. So it's a 17'8" boat now? Any ideas? Stations are 19.5 inches apart. Transom is angled about ten degrees. Ed

when I learnt to loft, i had the help of HOWARD CHAPPELLES book,
it has stood me well over the years and all boat builders really should read in order to grasp the thing properly
you are going well, I would urge you to seek it out, and dont settle for 1/8 or even one mm, get it right you can do it
in fibreglass, sure you can fill it up with bog!! but how satisfying is that? In metal we try get -.5 mm, and NOTHING over which will produce a bump, which is hopeless cos then you have to bog the whole job out to that bump
http://cgi.ebay.com/NEW-Boatbuilding-A-Complete-Handbook-of-Wooden-Boat_W0QQitemZ350182148657QQcmdZViewItemQQ_pidZ215246QQ_mediaitemZ1QQptZUS_Nonfiction_Book?hash=item350182148657&_trksid=p4295.c0.m312&_trkparms=240%3A1318|301%3A0|293%3A1|294%3A50
buy it PLEASE
if you do not I will, lost my copy

[Petros]

What you wrote seems reasonable and seems like a good approach. I would not worry about it too much, you can always shim or trim the moldes after it is assembled if it does not quite fair the way you expect. Minor adjustments of 1/8th of an inch or so will not likely have any noticable effect on how it behaves.

I have found even with professionally prepared plans there can often be parts to the hull that do not quite fair and most end up trimming and shimming the molds until it is fair anyway. I would not worry too much about and just get started on it.

It seems to me in the schools there is a lot of obsession with symmetry, many hours are spent on a cold molded hulls for example, getting each half exactly symmetrical with the other half. The more i thought about this, at least on a sail boat, the more I think it is a waste of time. Make it fair smoothly yes, but on a sail boat the hull is never symmetrical in the water anyway, except in the rare instance you are going strait down wind.

So I think symmetry is overrated, and slight variations in symmetry will never even be noticed. I have even seen some larger old wood sail boats that are noticeably NOT symmetrical with the eye, and they sail just fine, sometimes the owner did not even notice.

So go have a good time and do not fret over it too much. What is your intended use, recreational day sailing?

[longfellow]

Thanks all.
I do have all five diagonals faired nicely and the LWL is good to, and it jives with the diagonals. To get a decent transom, I did fair two buttock lines but only in the aft section of the boat. Likewise I also faired all of the WL's but as I said they don't hit all of the marks and I refused to compromise the great looking buttocks. So I used the WL's forward, where they are closer to the marks anyway, to get my stem rabbet bevels. It looks like I should make the fwd face of the transom heavy and I am stuck with a bit of 'fit and trim.' That's what I get for not truly working it through to get all three views perfect. I agree, to make the transom plumb will take away too much of the beauty of this daysailer. Ed

[Landlubber]

Yeah CHAPPELLES book certainly is an oldie but a goodie, and as far as boatbuilding goes, oldies are goodies. There is NOTHING, new in boatbuilding other than the materials and fastenings, the lines, constructions etc etc are as they have been for centuries, shapes come and go, but the basic stick it all together is really best learned by books like Chappelle and getting ya hands dirty.....nice to see you are getting dirty hands......enjoy the trip, it has only just begun.