Checking she's square...

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pauls_SPT

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Checking she\'s square...

Hiya,

I'm rebuilding a 41' double-diagonal built seaplane tender from about 1935(ish).

The decks had totally rotted through and I've removed them, as well as the superstructure, leaving nothing but the hull and deck-beams.

Before I go relaying the decks, though, I want to check that the boat is straight and square - I'd be prepared to bet that, with no decks etc, the hull's about as stiff as a jelly...

She's in a boatyard, sitting on a pile of wooden blocks and a ply frame I inherited from the previous boat that was there, so I couldn't guarantee that she's level, not twisted, not hogging or sagging...etc etc etc

Has anybody got any ideas? I wondered about tying poles fore and aft and seeing if they lined up, or firing a laser from end to end and seeing what it looked like...

Any help will be much appreciated,

Thanks,

Paul /forums/images/graemlins/confused.gif
 
Re: Checking she\'s square...

I don't think that you need the complexity of lasers. Can I suggest a string line [builder's twine] stretched between the centre of the transom and the stem head. This will give you a centreline. Level the boat transversely from gunwale to gunwale with a spirit level on a beam. If this is done at several points along the hull twist will be revealed. A plumb-bob suspended while touching one side of this centreline and touching the keel should confirm if there is any twist in the hull. Getting the thing set up correctly is fundamental to the success of the rest of the job. Also measure from centreline to gunwale at many points along both sides to see if the two sides are the same shape. To make sure that you are measuring truly square to the centreline, measure from the stemhead to the point on the gunwale on both sides and ensure that they tally. This will keep you off the streets and out of the pubs for a few weeks.
Peter.
 
Re: Checking she\'s square...

If there is an error, you might try counting the planks on each side. On a boat that I looked at recently, a friend noticed that there was an extra plank on the starboard side. /forums/images/graemlins/crazy.gif
 
Re: Checking she\'s square...

/forums/images/graemlins/smile.gif
But she's double diagonal...

I'm pretty sure that the RAF built her right, I just want to get her straight before I put new decks down...
 
Re: Checking she\'s square...

I've seen professionals taking a LOT of time and care over this part of the process, espescially with largish motorboats.

It was explained to me that the savings in getting the hull absolutely straight and level are immense - the time saved later well repays the initial care in chocking the hull dead straight and level.
 
Re: Checking she\'s square...

Hi pauls_SPT.
I can't agree more with Peterduck he's got it spot on.
If it will help I would like to add make certain you are lining her out to her water line and not just the topsides. When you have got her set up and levelled both ways side-side and fore-aft.
A spirit level set up as a sight on a camera tripod 30/40ft away at water line hight so it will swing true will do the fore to aft job again to the water line, (in 1990 I used a telly air gun sight set up to swing true on a video tripod no cheap lasers then I have since bought a laser kit including tripod in a carrying case (Chinese I think) off ebay got it for £15 and it proved my original settings were good) better if you can beg or borrow a laser set. Then firmly chock her add props fore and aft if she has long overhangs and a counter stern. Don't force to much weight on the for and aft props If you can set a line try to get some thin steel wire (Farm suppliers) set up with a tensioner for (easy removal) under the deck beams and mark the under sides a white patch and a black line is seen easily you will know as soon as you pull her off line. Mercia III has been lined up this way and is still on her chocks it helps with all the internal furniture line out to have her true and level. see G.U Laws and Mercia III.
Hope this helps Cheers and all the best with your refit
PS can you post a photo.
 
Re: Checking she\'s square...

[ QUOTE ]
But she's double diagonal...

[/ QUOTE ]

Doh!!! /forums/images/graemlins/blush.gif
 
Re: Checking she\'s square...

Thanks everybody /forums/images/graemlins/smile.gif

Here's a picture for those who are interested...you have to imagine this with no superstructure and a big green tarpaulin instead...



Paul
 
Re: Checking she\'s square...

Yes a nice looking hull you will need plenty of supporting planks protected with carpet is the usual way on blocks under her make sure the wight is well spread and not just on small spots. I think the line out will be how she looks on your deck beams, gunwale and shear strake rather then following a what looks to be a none existent water line. If their is one it will help a lot to level her to it. Jacking and packing to the marks you set up on her deck beams as Peterduck advised with the string to get her true.
She will have good sea keeping and be fast.
When we found Mercia III she had a site cabin on top as well.
Are you going to put her back in her original topsides layout.
 
Re: Checking she\'s square...

looks like a RAF 200 class.

better work fast, i heard the boatyard is being sold to make way for a petrol station for a major supermaket !
 
Re: Checking she\'s square...

Try using a boat level /forums/images/graemlins/grin.gif
Or you could set out lines around the boat to give you a level datum , then you could take measurements each side first to find out how she is sitting and then this will give you how far out she is sitting so you can adjust any further measurements to allow for this . In effect making say the rubbing strake or whatever part you choose your datum line .
 
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