structural concern

[Raf]

Hi all.

I've found a tiki 30 for sale and considering to buy it but, the boat wasn't build by plan and I am much puzzled about the engineering and structural strength. The boat is made of fiberglass over foam. Problem 1) There are 7 aluminium beams 100 mm x 50 mm rectangular hollow section 6 mm wall, 4' x 2' x ¼. fiberglassed straight to the hulls, three of them are also bolted. My concern here is that the aluminium covered by the glassing cannot be checked and aluminium oxide could form unseen and deplete the strength of the beams. Is the section of this beams adequate?

Problem 2) the beam at the bow holding the trampoline is made of a 50mm diameter pipe, 2'. It seems to me that this pipe is too small and will crash at the very first time the bows dip in and scoop water up. Right or wrong?

Problem 3) at the stern, a board has been placed across from hull to hull, half way up from the WL to the beam in order to facilitate boarding. Wouldn't this board splash hard on the water when the boat is pitching?

Any suggestions are much appreciated.

Cheers.

[Rogerio Martin]

Too many modifictions on one boat. Not good deal. Scott Brown have one good Tiki 30 for sale...see:

http://www.multihulls.uk.com/index.php/wharramcats/1274tiki30

[Raf]

Thanks Rogerio. I think you are right. Too many modification to the original plan and they don't seem to be neither  improvements nor reliable to me. Would much appreciate the comments of other Wharram knowledgeable people as, I need to justify my offer to the owner. That boat needs a all refit to the deck and beams and my offer will be accordingly.

Thanks for the link, looks very interesting but I am in Australia. A bit too far.

Asta la vista 

[Rogerio Martin]

You welcome...I don't know how much you wanna spend, but here have one good Tangaroa in Adelaide

http://www.gumtree.com.au/s-ad/adelaide-cbd/sail-boats/37ft-wharram...

Raf said:

Graças Rogerio. Eu acho que você está certo. Muitos modificação ao plano original e eles não parecem ser nem melhorias nem confiáveis ​​para mim. Seria muito aprecio os comentários de outras pessoas conhecedoras Wharram como, eu preciso justificar a minha oferta para o proprietário. Que o barco precisa de uma reforma tudo para o convés e vigas e minha oferta será de acordo.

Obrigado pelo link, parece muito interessante, mas eu sou da Austrália. Um pouco longe demais.

Asta la vista 

[Shaun]

Hey there Raf,
JWD designs various boats to be built to their specific plans and modifications of a designers plan needs to be assessed and approved by the designer to ensure the structural integrity, therefore safety, is not compromised. These boats absorb the stresses of pitch,yaw and roll through beam to hull lashings, a progressive transfer of load.
The hull skin and the framework within create a monocoque chassis designed for a that progressive load transfer, who knows if it will tolerate higher shock loading that a rigid structure will provide.
Flexible connection vs rigid, two concrete blocks each with a crowbar poking out. One is embedded directly in the concrete and the other is sitting in a rubber bushing now belt the crap out of the crowbars with a sledgy and see which joint gets loose first.
Additionally, the two hulls move at different pitch rates which creates torsional loading at the beam to hull connection, on this boat this rigid connection has a cross section of only 100mm x 50mm.
The joints may hold on for quite a while not even showing signs of failure then again as you mentioned they cannot be checked and if they fail at sea in a storm....
Problem 1, I think you nailed the answer in that the integrity of the joint cannot be checked and they are well outside of design specs.
Problem 2, the pipe should not compromise the structural integrity of the boat as a whole and it should be easy enough to rectify.
Problem 3, if the board is adhered rigidly to the hulls, glassed and filleted, and it breaks due to slamming you would end up with two separate pieces being forced up and down trying to destroy the joints that are holding them to the hulls, which are the very things that keep you on top of water rather than in it!
Please be careful with this one, if it can be returned to within design parametres and the cost is appropriately low...?
Be cautious,
Shaun

[Raf]

Thanks Rogerio. The Tangaroa 37 in Adelaide and the Tiki 30,discussed in this thread, are the 2 I am considering. Thanks Shaun. You surely have hit the nail in the head here. I am a boat builder with many miles on the clock but don't have the verbal skills you do. English is not my mother language. I tried to explain to the owner all the wrong things of his boat and my offer was accordingly to cover the work to rebuild the beams and deck to specs. the owner has taken it as an insult. As you say the beam at the bow and the boarding plank can be removed and are not dramma but, those beams, fiberglassed straight to the hulls are a total nonsense. A recipe for troubles, a disaster to come. I have 35 years of sailing experience and gone through a few of those treacherous conditions the sea is capable of and my imagination runs wild, thinking of that boat in those conditions.

Yes Shaun, I am cautious. 

Thanks. Cheers.