Bending hollowback stainless around bow

[Scott Dufour]

Rocinante's (CS17 #110) starting to show a little wear from the unforgiving ramp I sail out of.  Just forward of where the keel (which is protected with UHMW plastic), she's abraded into the fiberglass.

I'm thinking of just putting some stainless steel half round from that point up to the bow eye.  How easily does the half-round bend around that stem?  I'm worried about it crimping or flaring out.  How tightly does it need to fit?  Should I use a bedding compound? 

In general, how's this work?

[Tom Lathrop]

No problem with bending hollow back stainless.  Just fit it in place starting with the sharpest bending area.  No need to pre-bend, insert one screw at a time and it will be fine.

[Scott Dufour]

Thanks Tom.  Will do.

[Hirilonde]

If a material can be bent into position, be it wooden toe rails, aluminum sail tracks or SS chafe strips like in this last question, then the simple procedure Tom mentions is the way to do it.  By starting at the end with the greatest bend (smallest radius curve) you have a long lever arm to use while bending into place.  In the case of toe rails I have even started with the piece being longer than needed to give me some lever at the end.  I then cut the excess off after installation.

[Scott Dufour]

So I've got another question about the hollowback.  Right up near the bow, where things are going vertical, the sides meet at a much more acute angle than lower down, where things flatten out a bit.  Is the normal procedure to order the hollow back to fit the flat, and then crimp it in as it moves up the bow, or order it for the acute, and pry it open as it moves down and flatter?

I'm confident when I work with wood, but I've been known to really screw up metal in a hurry.  And at $40 a mistake, I can run through funds in a hurry...

And finally, those of who who know the bow of the CS17, what size oval hollow back should I order?  It seems to come in 1/2" to 1 1/2" sizes in 1/4" increments.

[John Burritt]

Do you have an exterior wood stem piece continuing forward from the keel?  If not, you might want to think about it to protect the bow. With that in place, the stainless hollowback can just continue upward using the same size.  I've always used 3/4 in. stainless.

[Tom Lathrop]

Ditto what john said.  In any case, I don't think trying to crimp or spread hollowback is what I would want to try over more than an inch or two.  Sounds difficult.  If your stem flat is too narrow for the 3/4" material, I think I would either go with 1/2" all the way or end the 3/4" under the bow where the stem starts to narrow.

Can't really tell without seeing the boat though.

[Scott Dufour]

I don't have an exterior wood stem forward of the keel.  Just the side/bottom panels with about 4 layers of glass.  (Is this one of those things I was supposed to know to do, though it wasn't in the plans?  Probably something a real boat builder doesn't need to be told...)

So if I've got this right, you two suggest an exterior piece of hardwood (probably white ash) faired into the existing keel and bent up to at least the bow eye.  Then I wrap that with the hollow back, if needed?

I guess that means planing a flat area around the entire stem to land the hardwood. (Or better, I guess, routing out a fitted opening bevel in the rubstrip.)   This is sounding a lot like work.  :-?

[PAR]

This is an inverted CS-17 I did last year. The bow eye is installed, but the 1/2" solid back half oval hasn't been installed yet. Note the landing area for the bow eye is about an inch wide, but the stem face is about 5/8" wide. Just big enough to install the half oval.

If you haven't made a "landing" allowance for the half oval (hollow or solid back) then you should consider so now. The only other metal option is a custom cut and welded V shaped affair.

[John Burritt]

You're already finding that the exposed edges of the bow can be sacrificial,  thus the need for the stem piece.  If you don't have wood that will bend to the curve, you can cut curved sections from as wide a board as you may have and overlap them with long scarfs.  The hollowback will add to the security.  Profiling the inside of the curve to fit the stem would beat reshaping it and destroying the integrity of the glass.  As you'll note from above, this is not a unanimous opinion.  Just one that works and stays looking decent.

[Scott Dufour]

PAR:  Yup.  That's exactly what I didn't do.  I covered the skeg with the UHMW plastic, but all protection ends there.  No flat landing forward of that. So you recommend grinding a flat and putting the solid-back half oval on?  That's probably the least painful option from the wood-fabrication point of view.  That will require me to grind through the glass and into the wood...  Should I re-glass the exposed area?  Will I now have a structural weakness without re-glassing that joint?

John: If I go with add-on-wood option, it's probably going to take a lot of thickened epoxy filler to fill up for gaps I will inevitably have... that means that I won't be able to just bed it in something removable.  If I put the hollow back over that, it this the kind of thing that's rugged enough to last many years?  How often do these sacrificial stainless steel protected wood backed bows get sacrificed?  

[wkisting]

Don't know if it will be helpful, but my write-up and pics of this process (using solid stainless half-round, not the hollow back sort) is on my webpage here: http://www.roguepaddler.com/cs20k.htm  (about halfway down the page, I think).

We didn't add wood to the exterior at the bow... just planed the bow seam back until it was 3/4" wide to accommodate the stainless width. We also drilled out the stainless to accommodate a bow eye passing straight through the half-round, instead of piecing in separate sections of half-round above and below the bow eye. Of course, we planned it this way from the start, so before painting the hull and installing the stainless, we did glass over the flat landing area we had planed into the wood to restore strength to the bow seam.

Hope that made sense.  

[PAR]

Yes, I planned the centerline seam (actually used a belt sander) to create a flat landing for the half oval. I searched high a low for solid back 1/2" and forgot about the bow eye. When the bow eye arrived, I was screwed so I epoxied two triangular pieces of oak to the bow, filleted them on and radiused the area, so it looked like I planned for it all along. This was all done before the hull was faired, then 'glassed. It does make the sheathing process a little more difficult. I used fairly tight radius on the flat spots, which pissed off the 'glass as it was trying to lay down, but some well placed staples fixed it.

If you use hollow back strips, they will dent when impacted and they will kink if you bend them too tightly. Solid back stuff is much tougher (and more costly). Because it's usually pre-drilled you have to be careful when you bend this stuff too as the holes will make the bend want to adopt a kink too. The strip is bedded in polysulfide rather then polyurethane.

[Tom Lathrop]

Paul,

I have been using hollowback on boats much larger than the CS and have not had any problem with denting the material.  Scratched from hitting concrete docks and such, yes, but solid would not fare any better in this regard.  The only problem related to the hollow shape I've found is that it will dent the wood behind more than the solid stainless would.  I would never choose the very heavy and very expensive solid strips based on 20 years experience in some rough service with the hollow strips.  

We often put 3/4" hollowback on both keel and mid chine area of BRS boats to prevent damage from concrete ramps and dragging over oyster bed beaches.

I have considered filling the back with epoxy to prevent the backing wood from denting though.

I doubt you would hit anything hard enough with a CS to dent the hollowback more than solid would.  That last is to cover the case where both the rub strip and the wood are deformed by a heavy contact with something solid.

[PAR]

I doubt you would hit anything hard enough with a CS to dent the hollowback

Agreed Tom, though it's usually the other way around when damage occurs. As a rule sailboats are driven at speeds not likely to cause this type of damage and they are also handled in a fashion that would preclude a good smashing at the rail.

On the other hand I've seen and repaired many of these types of hollow back rubs over the years and they are almost universally mashed by a powerboat. These are often are driven at speeds and commanded in such a fashion, that a smashed hollow back might be the least of the owner's concerns after the incident.

[wkisting]

Par wrote:

Solid back stuff is much tougher (and more costly). Because it's usually pre-drilled you have to be careful when you bend this stuff too as the holes will make the bend want to adopt a kink too. The strip is bedded in polysulfide rather then polyurethane.

I just want to echo Par here... As the article I linked to points out, we had to custom roll our stainless at a local machine shop, getting it to match a cardboard template of the bow curve BEFORE drilling holes. We nearly wrecked a piece trying it in the opposite order first, and got kinks at the drilled holes just as Par warns. (We ended up being able to salvage the kinked piece for something else, but not for the boat). Drilling holes in the curved piece then becomes a bit of a pain, but can be done well (ours came out nicely) if you clamp the piece securely in a drill press and work slowly.

Also, since half-round (solid back) stainless is expensive, we used a 6' piece of half-round only at the bow (the cosmetically visible portion), then switched to 1/8" thick stainless flat bar (3/4" wide) to line the rest of the keel thereafter. Works great, looks great.

For greater ease of drilling and bending, I'd probably try going the hollow-back route next time around, so if you haven't bought your stainless yet, it sounds to me like the hollow-back involves fewer potential hassles and less cost.

[PAR]

In the most recent builds, I've used T-6 aluminum flat bar stock instead of half oval. I can get this in any width and thickness I want, it's very easy to machine and it absorbs damage well to. I usually radius the edges generously and put points or heavy rounding on the ends to stylize them to a degree. It polishes and buffs well, though admittedly not to the degree of chrome, certainly as good as most stainless strips.

Some builds like mahogany runabouts, just demand the use of chrome. The best for this is brass or bronze half oval that's chrome plated. It'll never rust and is easier to bend too.

[Hirilonde]

The chafe strip on the keel of my Spindrift is solid bronze half oval.  I picked up a used section for peanuts.  The nice thing about bronze is that there is virtually no difference between new and used.

[Scott Dufour]

I really like the idea of using the aluminum bar stock.  Rocinante's not the type to covet fancy-pants; she's a low maintenance gal.  Aluminum's something I can work with easily enough.  I'll check it out.  If I do go with aluminum, what should I use to bed it?

[PAR]

When I install aluminum strips, I mark out for pilot holes on 6" (usually) centers, but don't drill them. I then place the strip on the hull, clamping with a ratchet strap or what ever works. I drill the first hole and run a temporary screw. 1/8" is easy to bend by hand around most stems or along most keels. Naturally if you have abrupt direction changes, you should put it in a vice and "talk" to it a little with a hammer or maybe some heat (be really careful with heat). I drill the pilot holes as I "walk" it on, then I remove, drill the clearance holes and counter sinks. Then it's just a matter of bedding (polysulfide) and screwing down.

A tip I use on all bedded pieces (hand rails, cleats, winches, etc.) is to very lightly start the screws and get some ooze out and caulking bead squishing. I let this sit for a day or more then go back and dog down the screws good. Now, I have a mashed piece of rubber rope under the part that also has adhesive contact, rather then tightening down on gooey adhesive/sealant and most if not all oozes out when tightening the fasteners.