|
Home
Why?
What?
How?
Tender
Cettia
Articles
Poems
Links
Contact
|
|||
 |
Building the Hulls - from Keel to Knuckle
Building the hulls using bead & cove Western Red Cedar strip-plank over a mould consisting of 19 frames mounted on
a strong back. The strip-plank shell is filled & faired using thickened epoxy and then glassed inside and out.
|
||
|
Building the mould. 19 frames are mounted vertically on a "strong back" of 6" by 2" timber. I was lucky to pick up the frames from Howard, another Eclipse builder in the UK - see my Linksweb page. Top of Page 
Use of a scarf jig to rout scarf joints for the knuckle "gunwale" Top of Page 
Planking starts from knuckle with first plank glued and fastened with silicon bronze screws onto the knuckle "gunwale". The glue used is an expanding polyurethane glue called Gorilla Glue, the excess of which is easy to scrape off. Due to excessive twist on the planks as they approach the transom, a change of planking direction is required - indicated by the plank laid over the "shoulder" of the aft frames. Top of Page 
Beginning the building of the outer stem laminated out of solid cedar and shaped to suit the boat. The outer stem is fixed to the inner stem. Top of Page 
The hull has had a coat of epoxy with gaps and gouges filled, and hollows faired, using epoxy thickened with Colloidal Silica.
Top of Page 
Three strips over keel and one layer of 600g/sq m glass cloth laid over hull down to the knuckle. The waterline and centre line are still visible. The position of the beaching keel and skeg was also marked on the bare wood and are visible through the glass. The centre line and keel/skeg positions has to be re-marked after 2 layers of cloth. Top of Page 
Beaching keel shaped and filled -ready to be mounted on hull. Top of Page 
Both skeg and beaching keel attached to hull using thickened epoxy applied to join and as fillets, or beads, around the join. Top of Page 
The cradle is fitted to the hull. The idea is for the keel to rest on the ground, supporting the hull, with additional support being provided by the cradle. The design of the cradle should make the hull easy to move: the cradle is jacked-up taking the hull with it; pipes are placed underneath enabling the hull to rolled forwards or backwards. Top of Page 
The first hull is turned over with the help of friends and family. The metal hoops are the beginnings of a polytunnel to protect the kiln-dried wood from rain, blown beween the slats in the barn during winter gales, and to provide an enclosed area that can be heated. Top of Page 
Richard scraping excess glue off inside of first hull. Planking of the second hull is now finished and it has been coated
with unthickened epoxy and filled with epoxy thickened with Colloidal Silica.
Top of Page 
The second hull is just like the first so there is not much new to photograph. So here is a cute picture of kittens in a woodshed. The farm has dozens of cats. The woodshed is next to the boatshed and these kittens are very curious about what we are up to. Top of Page 
The finished second hull is raised onto trestles so the frames and strongback can be removed. The timber from the strongback is used to make the cradle to take the second hull once it is turned over. The first hull is now almost completely sheathed with glass cloth cloth wetted out with epoxy. Top of Page 
The second hull in its cradle. We had 7 to turn it, but 6 would have been done: one at each end and 2 either side. Top of Page 
Both hulls now glassed on the inside in four stages: one coat of epoxy over bare wood (plus thickened epoxy for gap filling & filleting), sand smooth then apply glass wetted out with epoxy, a light sand followed by 2 more coats. Hulls are now ready to receive bulkheads. The polytunnel has now been lined with bubblewrap to give more insulation. Top of Page 
For the 2nd season, I raised the waterline using the same epoxy mixture and kept Swing Cat on a floating berth in a marina. The marina was locked, with free flow 3 hours either side of high water so, the water was pretty stagnant for much of the time - just the sort of conditions Sea Squirts love. At the end of the season the fouling was extreme. Apart from the Sea Squirts we had barnacles and weed. Top of Page 
|
Levelling the frames using the waterline given in the plans and marked on the frames. Top of Page 
Mould finished, ready for planking. Knuckle "gunwale" scarfed into one timber. Note inner stem laminated from 4 thicknesses of
marine ply. A bevel has been cut into the knuckle "gunwale" to take the first plank along the line of the curve of the nearest frame.
Top of Page 
Even with the change of direction of planking there is still a lot of twist over the last two frames, so desperate measures are called for! Top of Page 
Planking and nose finished and sanded. Screws show the centre and waterlines, prior to marking them out. Top of Page 
After a thorough sanding, the first of three 300mm glass strips is laid along keel, from stern to stem. Each strip has 3 coats of epoxy: one to wet out the 600g/sq m cloth, the next to fill the weave and the third to get a good finish. The first is applied using a stiff brush. the next using a plastic squeegee and the third using a roller. Top of Page 
The beaching keel is a laminate of solid Western Red Cedar planks. The plans give the dimensions of the top and bottom planks. The thickness of the planks available meant 3 intermediate planks were required. Templates were made out of 6mm MDF board for all 5 planks. The templates were used to rout each plank. Once all planks were laminated together, shaping to the correct profile is easy. Top of Page 
The skeg is also a laminate of solid Western Red Cedar planks. The wedge-like shape is given in the plans, but it also has to be shaped to fit the curve of the hull. Top of Page 
The keel has now been covered with four layers of 600g/sq m glass cloth and faired into the lines of the hull. A cradle has been built to take the hull when turned over. Top of Page 
The hull is ready for turning over. Below the waterline has had 4 coats of epoxy mixed with copper powder in the ratio of 1:0.8 by weight. The copper provides a hard surface and provides anti-fouling properties. Above the waterline has been treated with 4 coats of epoxy mixed with a green pigment paste, in the ratio of 1:0.05 by weight. The colour is close to the final colour. Final painting and anti-fouling will be carried out just before launching (which seems a long way off!). Top of Page 
Planking on the first hull is started by Owen. Notice, the polytunnel is now finished. Top of Page 
Mac marking the waterline, to give us a level to work off when fitting out the hull. The waterline was taken from the plans and marked on the frames originally. When the planking reached the waterline, we marked it onto the inside of the covering plank. Mac is now "joining the dots". Top of Page 
I usually walk to the boatshed, along a river, over a disused railway track, past a sewerage farm (OK, this ruins the image, but I must be truthful) and through fields containing bullocks, cows or heifers. This is a photograph from that walk on a cold, frosty, misty winter's morning. Top of Page 
The mould (frames & strongback) now removed and countless dollops of glue scraped off the floor! I found, when fitting the cradle, that the second hull did not have the same shape as the first. How could this be - the mould had not changed between constructing the first and second hulls? It finally came to me in the middle of the night! Freed from the mould, the hull was free to take a shape dictated by its internal tensions. The first cradle had been fitted while the hull was still on the mould. Phew! I haven't got an asymetrical catamaran. Build the second cradle identical to the first and all would be well. Top of Page 
A proud team of boat builders! From left to right: John, Richard, Owen & Mac. Top of Page 
My original idea for antifouling was a mixture of copper and graphite powder mixed with epoxy and thinned with methylated spirits. It was truly horrible to apply. The first season was spent on a mud berth. When Swing Cat was hauled out for the winter you can see fouling above the waterline and barnacles attached to the part of the hull that had been sitting in the mud. Some weed had attached itself to the epoxy mixture in-between but not everywhere. So a partial success. Top of Page 
For the next season (2020) I applied the commercial product Coppercoat. This is a water-based epoxy using a lot of very fine copper powder. Being less hard than my original epoxy mixture, the copper can leach out giving superior protection. That is the theory. Because this was a Covid-19 season, the boat was not in the water for very long and it is too soon to say if it has worked. My gorgeous helper is my daughter Henny. Top of Page |
||