Hull alignment and crossbeam position

[Cute Helles]

I had to dismantle my Tiki 46 and lift the crossbeams in order to change the pinholes on the crossbeams according to the design. Those crossbeams had pintight holes before, and in addition where heavily forced into the beamthroughs with hardwood wedges, hence lost any flexibility. It appears that the builder did not trust into the lashing.

Trying to reassemble them, I now become aware:

That the crossbeams do not sit flush on the inner hardwood pads of the beam throughs, when the hulls are absolutely vertical (measured by dropping perpendiculars on bows and sterns). Instead they show distances of up to 2.5 cm from the pad. In addition, floors and seating benches are not horizontal, but decline towards inside.

I wonder whether I should just skip the hulls to outside to allow the crossbeams to sit flat and the floors and benches to be horizontal? But then the stems and sterns would not be vertical, and the hull decks would decline towards outside, too. Or shall I just fit hardwood spacers between crossbeams and inner beamthrough pads, accepting that floors and seats are declining to inside, and that crossbeams would be even more above deck level?

Even more difficult is the finding that the hulls are not parallel when the crossbeams are pinned.  The distance from keel to keel in the front is 12 cm more than on the rudder skegs, positioning the hulls in almost a V geometry.. I assume  a bit of deviation is to be accepted, but 12 cm appears too much to me. What are your tolerances with parallelization?

Would you agree that I should exchange the hardwood inlets with the pinholes in the beamthroughs, if parallelization of hulls and thus change of crossbeam position will make changes in pinhole geometry necessary?

Anyadvise or opinion would be very much appreciated, since I feel a bit lost with this.Kind regards, Helles

Tiki46 APSARA

[john james]

CuteHelles-don't worry be happy-I should think the 12 cm over 46 foot boat length is not so bad. I would endeavor to bring the hardwood pads all into play .I mean the crossbeam should be resting on all eight of them as much as your patience will indure- I don't see why you should worry wether the hulls are vertical or not . Imagine if you had a mono hull it would never be vertical in the water certainly not when it's sailing.

[Brad]

I've built another design catamaran, so I can only comment on the keel alignment on that build. But 12cm of difference from the front keel centerline to the rear keel centerline is WAY too much. You are pushing a wedge of water sideways in addition to going straight ahead. The boat wants to spread itself apart. This will ruin any good sailing ability.  Your hulls should be parallel.  On my 34 foot catamaran the centerlines of the keels were off by no more than ONE cm from front to back. You need to get the hulls parallel before you do anything else.Then line up everything to that. 

Brad

[john james]

1 CM serious I think Brad is taking his James wharram plans a little too seriously.I dont Think the ocean is going to be that fussy 10 centimeters over the 46 foot lengths of the boat is not going to make any difference. I would think it would be a very time-consuming troublesome thing to correct---perfectionism is a particularly cruel form of mental instability

[George Ray]

(A) Did you get the building plans with the boat and if so they should reveal the thoughts of the designers on appropriate alignment/precision. (B) there are a few members with very serious building/sailing credentials whose opinions I would particularly seek out ( Ann-Neville & BoatSmith come to mind) (C) Email designers

My personal thoughts: (1) parallel hulls require the least energy to push through the water , (2) plumb hulls with flat/horizontal surfaces at rest may not be best. Boat sail with slight heel and flat surfaces hold some water rather than drain

John James has a point to consider, "don't let the perfect be the enemy of the good". The trick is knowing what is good enough.

[Robert]

Hi Cute,

you have about 0.5 degrees of toe out, which is regarded as acceptable toe out for many cars, so I would not worry about that if it is going to be a lot of work to change.  As far as I can tell there is no list of acceptable tolerances in the Tiki 46 plans; I am building hull number 43.  I work to the tolerance of what is not easily visible on the scale of the boat, this helps to get things done and keeps one from going insane obsessing about the fact that things do not quite work as the plans describe (probably due to an earlier measuring error ).

I would keep the interior level and forget about the stem and the stern being vertical.  Do try to get all the beam pads to make contact, if needed redo or modify them.  This is important to distribute the loads evenly into the beams and hulls.

Robert

[Brad]

One cannot build a boat perfectly. Errors in measurement will be made but most will cancel each out in the long run. That does not mean we should be sloppy in boat building. If the two hulls are aligned the boat slips through the water with the least effort. Does it matter if we can go a quarter knot faster? In a thousand mile journey? Does it make a difference?

[boatsmith]

Lining up the hulls parallely, plumbly, and square  is a bit of work. It is certainly possible that someone stopped at fugingudnuf.

120 mm is 4+ inches  is way more than I would allow. We plumb up the sternposts and stems. We measure elevations and centerline beams at the 4 corners. Then we measure the diagonals for squareness. Sometimes it is a little fussy. We usually are under 1/8" 1.5mm. 

It looks better when things are straight. Probably faster too.

[Bertrand FERCOT]

Hello cute

Sorry but I can't understand exactely the modifications of the builder. Can you post a few pictures?

For me 12cm is too much but to reduce it you have to modify all the beam holes!

As I explained in my Tiki46 building blog, I think more logical to have only holes (reinforced by a stainless tube) in the beams instead  slots and to have the slots in the bulkheads. Since her launch I sailed 18000NM mainly offshore without problems.

Bertrand

[Rob and Beth Boase]

The 12cm off parallel over 46ft is 12cm too much in my view. That amount of toe in or toe out must affect performance and if nothing else would create some interesting whirlpools behind the boat at speed! 

To set our Tiki 30 hulls square and parallel we first marked out a square on the floor(using the 3,4,5 method).

Then marked out the required measurements on the floor and used a plumb-bob suspended from each stem and stern post to line up with the marks. Our building frames were on castors so it was easy to manoeuver the hulls around. We managed to get the hulls square and parallel within a couple of millimetres.   I admit it would be more difficult with the hulls of a tiki 46.

Rob

[wakataitea]

i would change it. you are since a few years now on this boatyard. this little more work will not change a lot but i belive that the boat will be better .... just do it... and don't worry after it anymore..

hans

[boatsmith]

It might be that the hulls were planked up with a twist in 1 or both hulls. This might make it impossible for everything to line up. 

If you can't plumb up the stems and stern posts at the same time this would indicate twist in the hull. 

Then you will have to decide what to favor. Nothing is ever perfect and these boats are more tolerant of poor craftsmanship than some others.

[john james]

Excuse me before I began  building a James Wharram  catamaran I did not know a millimeter from a centimeter and I still don't very well, I was thinking  12 mm alignment rather than centimeters. Certainly as a builder this is probably too much of a an error And as a builder I would not tolerate it However that's not exactly the question;Cute is not building a boat he's got it hauled out in Malaysia somewhere The temperature is probably 80 or 90° Probably his box of hand tools sitting in the sun are  too hot to even touch. He's doing maintenance work. As long as he owns the boat he'll  do maintenance work, I believe the boat is quite  a new to him ,It's a piece of maintenance that would be extremely aukward and time-consuming to repair. Personally I don't think it would make much difference anyhow. That's why I say go sailing don't worry be happy.