Category Archives: rubbing strakes

Replacing the strakes (part 3)

After drilling and welding the new stainless steel strakes it was time to mount them on Tammy Norie.

We drilled out the old rivets and so there are no new holes in her hull-deck joint. Instead I drilled the holes to 6mm the smeared epoxy filler inside. The idea is to correct for errors in hole positions, allow the machine screws to tap a thread, and seal the fibreglass. Correcting errors is important as it allows the screws to share loads when the strake is functioning as a huge chainplate for a series drogue.

I also dug out most of the old dirty mastic sealant in the hull-deck joint, finding several quite large voids on the starboard side. I sealed the gap with Sikaflex and carefully squirted plenty of extra up behind the joint and into the voids.

IMGA0588

When the Sikaflex was tacky I folded a length of damp proof course padding in half so the fold was at the top and taped it approximately in position. The idea of this layer is to provide some protection between the hard steel and the softer fibreglass. (Also, if anyone asks what it is I can casually tell them it’s the damp proof course.)

IMGA0578

Suspending the strakes with bungees I pierced holes in the damp proof course, squirted some Sikaflex into the holes for a final seal, and screwed in the machine screws, tapping a thread into the epoxy filler. This was good enough to hold the strake tight while I added penny washers and nyloc nuts inside the boat.

IMGA0582

Then I trimmed off the excess damp proof course by sliding a thin piece of aluminium behind it and cutting with a knife.

Finally, I scoured the strakes with an orbital sander to clean them up and give an even light grey lustre.

Job done, ready to launch the next day.

IMGA0590

We’ll see how it all holds up over this summer. As I mentioned before, illness will be limiting my sailing this year, so it’s very unlikely the strakes will get a thorough loading test. I’ll write about any problems that do appear on this blog.

I’m very pleased with the result so far.

Advertisements

7 Comments

Filed under drogue, Repairs and Modifications, rubbing strakes

Replacing the strakes (part 2)

Today I learned to weld.

I drilled and fitted the port side strakes in Replacing the strakes (part 1) and yesterday I drilled and fitted the starboard side in one afternoon, having gotten the hang of it. It also helped that my cobalt steel countersink arrived. It cuts stainless steel like butter.  I was able to countersink about 30 holes in seconds each, without any sign of it blunting.  The only tip I have to share is that it’s a good idea to cut the entire depth you want fairly quickly in one push.  If you stop the stainless steel hardens and it’s a little tricky to get started again.

The next job was to join the two parts of the strakes on both sides. You may remember that we were only able to get 4m lengths of stainless steel bar, but the strake is 6.25m long. So the stern section is a full 4m and then we need to join the extra 2.25m. We decided to weld. Here’s an example of the joint before we started.

IMGA0512

After a quick shopping trip for some safety equipment, Dad showed me how to set up the welding machine, and I did a couple of practice runs on an old steel tube.

IMGA0536

IMGA0537

Then I took a couple of offcuts from the strakes and chamfered the ends to make slots to take new metal from the welding rod. The goal here is something of a compromise between strength, safety, and looks. I want to make sure the two parts of the strakes aren’t rubbing, and don’t have sharp edges or a slot to pinch skin or catch debris. The join will perhaps help to take further load from the series drogue or other attachments, but probably not very much. And finally, my goal is to make an invisible join.

IMGA0546

IMGA0547

Here’s how we set up to weld, using a jumper cable to ensure current reaches both parts.

IMGA0551

Here’s the result of the practice weld of stainless steel. Not too bad!

IMGA0553

I experimented with grinding of various amounts of metal to see what kind of finish I might get.

IMGA0554

We also attempted to break the weld by putting it in a vice and bashing it around with a hammer.  We did manage to crack it slightly, but decided it was strong enough.

Then we set up the two parts of the starboard strake for welding.

IMGA0563

Here’s what the inside of the strake looked like after welding and grinding.  This side won’t be visible so we just have to make it reasonably level.

IMGA0565

Turning over the outside was quite blackened by heat.

IMGA0566

I cleaned it up, welded, ground, and roughly polished the outside.

IMGA0570

Not bad, if I say so myself!  Once mounted on the boat it’s going to be pretty invisible, especially when we polish the rest of the strake. It’s already hard to spot.

IMGA0571

Tomorrow we will mount the strakes ready for a weekend launch!

1 Comment

Filed under drogue, Repairs and Modifications, rubbing strakes