Bot­toms up

This month, the Se­cret’s struc­ture is fin­ished off with the ad­di­tion of bot­tom stringers, bev­elled chine bat­tens and fore­foot cheek pieces. Ben Meakins re­ports

Practical Boat Owner - - Contents -

Ad­ding bot­tom stringers, bev­elled chine bat­tens and fore­foot cheek pieces to our Se­cret 20

Hav­ing per­formed the heart-in-mouth process of turn­ing all 400kg of the boat over last month, and hav­ing com­pletely re­assem­bled our garage, we could get stuck in to fin­ish­ing off the struc­ture. This con­sists of bat­tens to house the in­ner edge of the bot­tom pan­els against the keel, bot­tom stringers to sup­port the pan­els and a set of bev­elled chine bat­tens, as well as fore­foot cheek pieces.

But be­fore we added any more struc­ture, we re­alised that the com­part­ments formed by the fore-and-aft and trans­verse frames would soon be in­ac­ces­si­ble. And while we’d hope they never get wet, it was worth seal­ing them up with epoxy to wa­ter­proof them, just in case they aren’t ac­ces­si­ble once the bot­tom pan­els are in­stalled.

This was a quick job, with two of us work­ing. We started off brush­ing the epoxy on but soon re­alised that this was not only too slow, but that it was putting far too much epoxy on the ply­wood. Things weren’t helped by the fact that we chose to do this on the hottest day of the year, with the mer­cury ap­proach­ing 30° – mean­ing that the epoxy was threat­en­ing to go off in the pot!

A foam roller proved a much bet­ter ap­pli­ca­tor and ap­plied a good, thin and even coat of epoxy. The wa­ter­tight com­part­ments are now sealed and ready to be en­closed – and we plan to paint out any that be­come lock­ers or use­ful spa­ces with bilge paint at a later date.

For now, though, we could move on to the rest of the struc­ture.

Fore­foot cheeks

First up came the fore­foot cheeks. These curved pieces of ply have a bevel on their lower edge, to which the for­ward hull pan­els will be at­tached. As such, they will set the shape of the bow sec­tion – of vi­tal hy­dro­dy­namic im­por­tance – so care­ful shap­ing was nec­es­sary. Once we’d made sure that they matched the curve of the stem and that each side would be iden­ti­cal, they could be in­stalled with epoxy and tem­po­rary screws.

These done, we could move back to the bev­elled bat­tens that run along the keel. To house these, we had to cut out a lit­tle of each frame where it met the keel be­fore screw­ing the bat­tens in, us­ing a piece of scrap tim­ber to en­sure that they aligned prop­erly with the frame edges.

The bat­tens had warped over the hot sum­mer, stored in our garage roof, so to make sure that the hor­ren­dous warp­ing didn’t cause bulges in the hull shape, we tem­po­rar­ily clamped a straight but flex­i­ble bat­ten to them to en­sure that they took up

a smooth curve. We used ex­tra screws in the prob­lem ar­eas be­fore re­mov­ing the straight­en­ing bat­ten – and a fi­nal Mk1 eye­ball, look­ing along the bat­ten, showed up any fur­ther ir­reg­u­lar­i­ties that could be taken out with ex­tra screws. Once all was epox­ied on, we didn’t need to worry about this any fur­ther – but it was worth spend­ing the ex­tra time on it to avoid swear­ing and painstak­ing chis­elling at a later stage!

Bot­tom stringers

The bot­tom stringers were sim­ple to in­stall – one of them went be­tween frames 4 and 9 so could it be housed in eas­ily enough, with no tricky bevels to cut. The other was trick­ier, re­quir­ing a com­pli­cated com­pound bevel where it met with the raked, curved tran­som. This we mea­sured with a slid­ing bevel at both ends, cut­ting the an­gle in square be­fore us­ing a sharp block plane to cut the bevels in the tim­ber. This done, the stringer could be clamped to the tran­som and housed into all the slots in the frames. There was a sig­nif­i­cant amount of twist re­quired at the bow, where the an­gle changed by around 45°, so for this we used a G-clamp as a lever to ap­ply the nec­es­sary torque while one of us fixed it with tem­po­rary screws – ex­tra-long for se­cu­rity!

Chine bat­tens

The chines on the Se­cret 20 are ini­tially in­stalled as a flat panel run­ning 2⁄3 the length of the boat, be­fore be­ing built up to give a rounded turn to the bilge. The stringers for these are bev­elled to the shape of a right-an­gled tri­an­gle – but the wood used, a light­weight an­tipodean al­ter­na­tive to Dou­glas fir, is splin­tery and prone to crack­ing – es­pe­cially when it takes up the curve of the hull.

The way around this was to cut nu­mer­ous kerfs in the back of the stringer, al­low­ing it to take up the curve of the hull with­out split­ting. We spaced these equally, around 2cm apart on the great­est curve, to en­sure a good, even bend in the wood, be­fore us­ing screws and penny wash­ers to pull the stringers right into the frame. Like the bot­tom stringers, these needed a com­pound bevel cut­ting on the end where they met the tran­som – and care was needed to line the chine edges up with those al­ready set by the shape of the tran­som.

The grand epoxy job

With ev­ery­thing dry-fit­ted, an­other ma­jor epoxy job dawned. The keel bat­tens needed re­mov­ing and glu­ing on, and each of the stringers needed fil­let­ing to the frames and tran­som. This done, the boat is even more solid than she was be­fore – and you can re­ally see the shape emerg­ing.

Next month comes a lot of fair­ing, with long­boards and long planes, to en­sure that when the bot­tom pan­els go on there are no hard points or lumps. The stringers are proud in places, and the bev­elled bat­tens will need fine-tun­ing with a bull­nose plane to en­sure the pan­els will fit on with­out any gaps.

...and screwed and clamped in place, mak­ing sure they were even on each side

The fore­foot cheeks were epox­ied...

We coated the in­side of each com­part­ment with epoxy to seal them up

We used a G-clamp as a lever to twist the stringers at the bow

On the chine stringers we spaced the kerfs equally, us­ing screws to pull the stringers into the frame

...and a fi­nal Mk1 eye­ball showed up any fur­ther ir­reg­u­lar­i­ties along the bat­ten

A sharp block plane proved ideal to cut the com­pound bevel on the stringers

Round­ing off the in­side edges with a router helped the stringers fit the slots

These needed a com­pound bevel cut­ting on the end where they met the tran­som

ABOVE We tem­po­rar­ily clamped a straight but flex­i­ble bat­ten to them to en­sure that they took up a smooth curve...

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