working narrow boat cross planks

[Dave Clinton]

What are the dimensions of the cross planks on a GU motor boat?

 

What shape is the cross plank that holds the mast box?

 

What wood would be suggested for outdoor use, as the original specification, Oregan pine, is difficult to obtain. Cedar perhaps?

 

If anyone could take a photo of the mast plank, it would help me enormously.

 

thanks, Dave

[stagedamager]

I've used Douglas Fir for Toplanks. Sourced it 12X2 and seasoned it. A plank came in at 60 quid delivered. That allowed for a bit of shrinkage and finishing to get to the correct size. No a union boat however.

Dan

[ChimneyChain]

The top planks are 11" x 1"3/4 so I was told.

 

Darren

[Leo No2]

Sculptor's (GU Small Northwich) are 11" at the mast cutout and 8" at the sides x 1.75" and I assume are in the region of 84"/85" long (7'). The taper is all on the rear facing edge - completely straight on the front facing edge.

 

Mast plank (1)

 

 

Mast plank (2)

 

Edited April 4, 2015 by Leo No2

[Timleech]

Sculptor's (GU Small Northwich) are slightly less than 9" x 2" (may be metric equivalent) and I assume are in the region of 84"/85" long (7').

I'd be worried if they were that long! Probably more like 75".

 

Tim

[Tony Dunkley]

That mast beam in the pictures above is all wrong . . . that's not how it was done.

The stern beam and middle beam were made of pine, but the mast beam was almost always oak, and not notched out like that because it weakens it too much. The sideways location for the mast was by means of two tapered chocks( long wedges really) spiked into the edge of the beam, or the beam was cut to that shape ( with the notch) from an extra wide piece of timber, with spikes on either side of it to prevent splitting under strain.

[davidg]

For the beams I would use iroko, it will outlast you.

 

Unfortunately if you make the planks out of iroko they would need a crane to lift them so use douglas fir, as already been suggested. I believe douglas fir/oregon pine are the same tree depending which side of the US/Canada border you come from, or something like that..

 

I would make the beams the same width as the outside of the beam chocks and step the ends in to fit inside. The mast beam is wider in the middle to accommodate the housing for the mast without chopping too much of the beam away, Sculptor's looks about right, could possibly be made a bit wider maybe.

 

They are usually done with ex. 2" sawn so as thick as you can get away with from that when planed up. I recently replace two of my top planks and to match the existing ones for thickness had to use 2.5" - ouch.

[David Schweizer]

According to the drawings of GU motors that I have, the cross planks measure 9" x 2" and as the OP suggests are specifed as Oregan Pine,

 

Oregan Pine is also known as Douglas Fir, and although originating from North West America, is now widely grown throughout Europe, and should be readily available from any good timber yard, Althiough one of the stronger softwoods it is still only classified as moderately durable. European grown timber is generally regarded as being more durable being grown more slowly than most UK grown timber.

Edited April 4, 2015 by David Schweizer

[Dave Clinton]

Wonderful. The collective knowledge of Canalworld.

 

Douglas Fir it is, 9 x 2 sawn for the standard planks and 12 x 2 sawn for the mast beam.

 

I must say I've yet to see a mast beam in oak.

[Tony Dunkley]

Wonderful. The collective knowledge of Canalworld.

 

Douglas Fir it is, 9 x 2 sawn for the standard planks and 12 x 2 sawn for the mast beam.

 

I must say I've yet to see a mast beam in oak.

 

You probably won't , if everybody's making them out of pine these days.

[David Schweizer]

 

You probably won't , if everybody's making them out of pine these days.

 

If the boat (and therfore the mast) is not being used for working then pine will be ok. However, I would not trust pine for a mast being used for towing, it does not have the lateral strength of oak, which is readily available from any decent hardwood sawmill (admittedly for a cost!)

[onionbargee]

Scaffold planks make good box masts. They are high quality selected timber for obvious reasons.

[Dave Clinton]

yes, I agree, unfortunately they are a little too narrow and too thin to do the cross planks.

[onionbargee]

Especially if they accidently fall off some building site into your boat as your passing, totally accidentally, by accident.

[David Schweizer]

Scaffold planks make good box masts. They are high quality selected timber for obvious reasons.

 

Most Scaffold boards sold in the UK are not of very high quality, even the so called grade A boards can be defective, and many are little more than sawn lumps of ungraded timber (knots and all). It is an industry wide problem, and whilst there are suppliers of board without defects, most that you can buy from a General Builder's Merchant are not of a very good quality, and are best avoided. The only boards worth buying are those produced to British Standard, BS2482: 2009, but they are a lot more expensive, and it would brobably be cheaper to source quality timber from a good sawmill.

Edited April 5, 2015 by David Schweizer

[Guest]

On 05/04/2015 at 10:41, Dave Clinton said:

yes, I agree, unfortunately they are a little too narrow and too thin to do the cross planks.

May I ask - what are the typical dimensions for the inner and the outer sections of the box mast?

I'm guessing 8" square outer and 6" square the inner?

Thanks

 

[billh]

8" is about right for the outer,  but 4 " for the inner.For  the latter  you should use a quality hardwood piece- a lot of  sideways stress on it when fully extended.Also, assuming you are making one, pay particular attention to the bottom of the outer- water can collect inside and cause rot very quickly.

[Guest]

Very kind of you Bill, much obliged