Wharram Builders and Friends

A Photo & Discussion Forum for Wharram Design Enthusiasts

This is the problem: The aft section of the boat (from aft end of keel to skeg end) seems to be distorted to the extent that there's a rise of about 30mm in the curve of the sheer line when trying to fit the aft section of the lower hull panels to the backbone. The curve of this part of the backbone is flattened by about 20mm in the centre compared to the panel. The panel doesn't fit the keel doubler and the backbone at all. Obviously not good, as the problem will make the measurements of the upper hull panels, bulkheads etc. a very tricky business and possibly even an issue when looking at the lines of the finished boat - it doesn't take much to spot a "wrong" curve. I don't think it's enough to impact the performance of the boat though.

I have included a photo of the very obvious problem - aft lower hull panel versus keel doubler!

At this stage it is not possible to check all measurements, however: the panels are spot on and every other measurement I can actually check are all within a couple of millimetres. I'm a fairly experienced boat builder and work to quite a high standard of finished work, which is not to say I don't make mistakes - everybody does - but I'm confident that all the pieces have been cut out and fixed pretty close to plan specifications. Even if you get one or two measurements wrong it would in most cases be obvious when for example connecting points for a curve. The one item I can't check other than visually, is the backbone, since both are finished and off the floor of the workshop together with the ply sheets they were measured up on (as per construction plans). The aft part does look a bit flat in the curve though, but as is drawn up from several measurement points is seems unlikely that I have somehow got it wrong to this extent.

Curiously, when fitted, the lower hull panels are overall some 20mm too long. Easy to trim off, but why? Certainly not because of not having measured and cut out the panels correctly.

The floor the lower hulls are constructed on have unfortunately been flooded three times within six weeks - up to almost half a meter over the floor (but not actually touching the ply and timber, other than stem and stern). This have ruined the floor and somewhat distorted the whole set-up. However, I have tried to re-align everything and the panels do fit reasonably well, at least from aft keel to stem. No particular problems here.

I wouldn't be building the boat if I didn't trust the Wharrams to produce reliable building plans, but I do know there are issues here and there. I just can't imagine this kind of error would not have been corrected long ago - after all, the T38 have been around for a very long time. I know that giving very accurate measurements for hull panels is not really feasible, too many factors are involved to make this possible. But what I'm experiencing would be errors, not just small variations due to the construction process. Unless other builders have had the same experience I'm inclined to discount this possibility.

This leaves me with the only possible explanation being somewhere in the build and shape of the backbone or perhaps a distortion caused by the flooding in some way I'm not aware of.

I know most of us would rather not reveal a problem like this out of fear of looking like a bumbling amateur and loosing any respect of your peers etc! But I would be grateful to hear from anybody having had similar sort of problems with a Tiki 38 build or perhaps being able to figure out what might have caused this horror of a building problem!

Cheers Klaus

Views: 910

Reply to This

Replies to This Discussion

I hesitate to reply because I have never even seen a 38 let alone built one. I would be surprised if the panel measurements were wrong. I do however sometimes build stitch 'n glue kayaks by eye or from very basic sketches and have some experience of offering -up panels, trimming and tweaking into the required shape and it sounds like the backbone/assembly is distorted. It takes very little to cause major changes in panel shape.  Double check the building base again. Have you a friend who might repeat this independently as sometimes we repeat the same mistakes ? Some times we have a "blind spot"?  Is there a general sheet to allow you to check the structure overall not just the individual parts ? You are right to do everything to get it right now or you could end up with a constantly accumulating error. There are really only two possibilities - either the assembly is untrue or the panel is. It would be a relief in a way I imagine if half a doz. builders said their panels did not fit either .....

Mate I think if I recall i had the same problem on hull two of my build.The only thing that comes to mind is that it could be as a result of the backbone/keel not being precisely curved as in the plans.

My problem was more pronounced in the bow area though.Where you notice it is when you come to place the crossbeams on their blocks. I think Wharram foresaw this and if i recall correctly the plans call for ''making the blocks to suit the individual positions they will occupy.Although this is for a t26 though.I thought of trimming the panels to suit but that would have had other consequences down the line.I also suspect that the ply I used on the the second hull being slightly thinner 0.5mm thickness may have had something to do with it.In the end it is not a major issue i feel and by no means a reflection of ones workmanship.Remember there are some planes and curves that have to come together precisely to make it fit.Aesthetically  you could not tell that the sheer lines are dissimilar on my cat unless you surveye them i am sure.

all the best paul.

Something that has come to mind, when scarfing/butt joined the panels together did you check that they were square?

Hi Klaus, it seems you are not alone in this, see Niel's problem on his Gleda.  He later on just filled in the gap and took steps not to repeat it on the second hull.  I am building a Tiki 46 and here the plan calls for making hardboard mock ups and only committing to ply when the hard board fits.

R

Hi Klaus, Oh Boy this brings back old memories...it was almost 10 years ago for me but what I recall is that there seems to be an error with lower bulkhead #6.  The instructions say to line up the ply planking with the bottom corners of the bulkheads,  and that works fine except for #6.  I found I had to raise the stern ply (two pieces scarfed) until it was 10mm above the #6 bulkhead corner,  and then it fit fine along the backbone.  My building floor was dead level,  checked with a builder's transit level.  All measurements were re-checked at least three times,  and no error could be found in my layout.  Both hulls had exactly the same result,  so there is no doubt in my mind that the plans are at fault.  In spite of doing this,  the knuckle turned out very fair when the upper planking went on.  And you do have to shape the butt ends accordingly,  can't just leave them square.  I am even more amazed than you that this sort of BS hasn't been corrected with so many built!

It's an odd experience...you have little choice but to stick to the plans,  yet do so without completely trusting them.  You will find yourself making the weirdest decisions along the way with serious doubts about the whole approach,  yet at the end wind up with a magnificent, beautiful boat.

Good luck with this,

-Alf

Thanks guys - your replies have been extremely helpful. I'm going full steam ahead again and will be fitting the first lower hull panels next week thanking the Great Epoxy God for her ability to cover up any mistakes on the path forward - mine and indeed the Wharrams (hope somebody there reads some of the entries on this website) !!!

Cheers Klaus

 I replied

I would be surprised if the panel measurements were wrong.

Well knock me over with a feather.

 It would be a relief in a way I imagine if half a doz. builders said their panels did not fit either .....

Must be a relief to Klaus and I am glad he has his answer and assurances.

But really as someone who has been using / helping others stitch 'n glue since the 60's I cannot see the sense here. That is to say the whole point of stitch 'n glue is that the shape of the boat is in the very very accurate panels. Once these are stitched together - there is your hull. The exact same hull every time. Accurate enough to permit the building of restricted class racing dinghies. This is where the speed is. This is where the time is saved. I cannot see this huge saving of time / weight / expense in this hybrid construction.  It seems this is not so much true stitch 'n glue as conventional building-on-a-frame with some stitch'n glue substituted to speed it up some. I cannot see it as truly fast. There is a fantastic amount of detail. Apparently the panels have to be offered-up marked and then cut ? No saving there.

For comparison, the sort of  times for true stitch'n glue, I built both hulls for an 18ft  beach-cat in a weekend. Not the whole boat but I had the two hulls. A friend built a 40ft steel Van-De-Stadt fast cruiser in a similar system ie. the panels were assembled fullsize to very accurate plans and then drawn together and tacked together to produce the hull shape the frames etc. only going in after. Result- a 40ft yacht in 3yrs of part-time work. And I mean Yacht as in suberb joinery fit-out etc. Since the "Boat" part of the build went so fast he was able to really do the interior / fit out.  [PYLADES - just back from 3 1/2 yr circumnavigation ]

True I am scaling-up from my experience with admittedly much smaller craft. But I have been thinking about this for a week now, looking at the photos on this site and peeking into the profiles of some of the contributors on this site, see how long since they started, when  [???] they might finish ? Fast to build ? Yes compared to a bridgedeck cat but it looks like a huge amount of building in the hulls.

Hi there - not entirely sure what your point is. If you got issues with the design of the Tiki 38 and the building process perhaps you should take it up with the Wharrams. I have built several boats, including a Tiki 21 about 20 years ago, in stitch and glue and would absolutely not like to build a 38' catamaran that way. There are very few stringers and framework involved in the construction of the T38, hence the wobbly nature of the boat at this stage, and I seriously doubt it would be faster and more accurate to stitch and glue the whole thing together. Cheers Klaus

Thanks Klaus.

I am thinking about building again as I would like more accommodation. The limiter as always will be budget - mostly hard cash but also time. I am trying to get a "feel" for modern methods as my P 31 is from an older building style. Thanks for the comments.

Klaus,

Your problem is not at all uncommon. Chuck came up with an appropriate saying for those building a Wharram:

ECAMOSVeritas

(Epoxy Cures A Multitude Of Sins)™ is Truth

Tee-shirts and hats may be soon forthcoming

Scarf in a filler piece, then mix up a good batch of epoxy with micro balloons and make a nice fillet. No one will ever know the difference.

Almost finished fixing the panels in place - looking Ok. Should probably get one of those tees and wear it at all times when building.

Cheers Klaus

Finished ! Lower hull panels and stringers in place and all is well thanks to the Great Epoxy God. Photos below. Now, of course, I will have to deal with a lovely Wharram Wobble. This seems to be a common problem and can be fixed with brute force. Very well designed, this part of the building process...!

Reply to Discussion

RSS

© 2019   Created by Budget Boater.   Powered by

Badges  |  Report an Issue  |  Terms of Service