Which would be less ugly?

[Chotu]

I have to stiffen up my roof a bit and add extra support.

I plan to extend my roof level davits quite a bit forward, across the whole roof to get additional stiffness in the roof. Just like stringers do with a hull.

Davits:

The davits have to be square tube due to the random direction of the stresses on the davits as the dinghy bounces around in rough conditions.

The square tube looks like this.





Roof Stiffeners/Stringers:

I could continue the square tube of the davits all the way forward across the whole roof. I feel this would be visually appealing. EXCEPT I need to drill a bunch of holes in it for through bolting it. That would look awful and be difficult to do. It would look like Swiss cheese.

Instead, what if I changed over from the square tubing to L channel as I carry forward? As in, square tubing for the davit part of the beam, then the cross section changes to L channel once the dinghy loads are no longer part of the beam and it’s just adding stiffness to the roof. L section is, of course, half the weight. It’s also easier to through bolt.


L channel looks like this.





Which one would be less ugly??

Is it ok to sacrifice looks a little to save half the weight and make something easier to install?

[rslifkin]

I think the square tube would look better if you can avoid bolt heads on the top and maybe filet the edges into the roof with some kind of filler.

I wonder if you could drill only the bottom of the square tube and use some kind of toggle bolt arrangement (upwards from the bottom) to avoid having to drill all the way through. Easier to avoid leaks that way as well, as the bolts shouldn't ever be exposed to water if the ends of the tube are closed. Maybe use adhesive to hold the tube in place as well for extra strength (and to help keep it all sealed).

[Chotu]

Originally Posted by rslifkin

I think the square tube would look better if you can avoid bolt heads on the top and maybe filet the edges into the roof with some kind of filler.

I wonder if you could drill only the bottom of the square tube and use some kind of toggle bolt arrangement (upwards from the bottom) to avoid having to drill all the way through. Easier to avoid leaks that way as well, as the bolts shouldn't ever be exposed to water if the ends of the tube are closed. Maybe use adhesive to hold the tube in place as well for extra strength (and to help keep it all sealed).

I was thinking of toggle bolts but was definitely concerned if they would be strong enough but also wondering if I’d be able to get the 25 holes to line up well doing it blind.

Looks wise, your idea is better than mine 100%

If I can pull it off...

[rslifkin]

I'd think big enough toggle bolts plus adhesive holding the tube in place should be plenty strong enough. If the adhesive used is paintable, then it would be easy enough to just glue the thing down and fillet the edges with adhesive, then paint over it all.

As far as hole alignment, you could drill the holes in the boat, then glue the tube down over them. Then drill upwards into the tube once the adhesive cures. That saves trying to drill holes in 2 parts and make them align.

[Chotu]

Originally Posted by rslifkin

I'd think big enough toggle bolts plus adhesive holding the tube in place should be plenty strong enough. If the adhesive used is paintable, then it would be easy enough to just glue the thing down and fillet the edges with adhesive, then paint over it all.

As far as hole alignment, you could drill the holes in the boat, then glue the tube down over them. Then drill upwards into the tube once the adhesive cures. That saves trying to drill holes in 2 parts and make them align.

Of course!! Here I am thinking about how to measure them out. It’s been a few years since I’ve been hands on.

I think your idea blows all of mine away.

Let’s go with your idea. It’ll look great! I’m getting FRP tubing for this.

[JebLostInSpace]

Originally Posted by Chotu

Is it ok to sacrifice looks a little to save half the weight and make something easier to install?

I will always 100% make that tradeoff, but then my Hunter 410 is no beauty. In my mind, I typically do whatever is strongest/best quality that I can afford. (Afford in both money and time) Then I look at making it pretty only secondary to that. Usually the marginal "prettiness" is more expensive and/or time consuming, and I rarely decide it's worth it.

That being said, if your boat is already very pretty, or if you have more flexibility in your budget (both time and money), or if you are more focused on resale value of the boat later on, then your calculus will likely be different than mine.


In this specific case, the better-looking square pipe is also stronger, so you have to decide if the extra strength is adding value for this specific project. From your description, it sounds like it does not since the load directions will be consistent and predictable on the new beam, but something to think about. If the extra strength of the square pipe makes a meaningful difference to the quality of the project, I'd say you should do it if you can figure out how.

Lastly, in my mind the L-bracket wouldn't look any worse the way I'm picturing it. But I've never seen your boat so could easily be wrong.

[Dsanduril]

If you can accept a bit more weight...

Get a piece of pultruded fiberglass bar, say 1” by 1/4”. Clamp it up against boat and drill holes through both. Over drill holes in bar to be sized to fit some rivnuts. Transfer bar to tube and drill holes in tube to get alignment. Put some rivnuts in the bar, with barrels long enough that they will be flush with outside wall of tube. Slide bar inside tube. Now the difficult part, with tube upside down, align rivnuts with holes in tube and get them to drop in (easy to write, a bit finicky to do). Using a few screws (they will be hidden in end product) attach bar to tube from outside. Roll tube over, put in place, and bolt to boat.

For an easier, but heavier again method, get a bar that is sufficiently sized to be the “washer” and do the same thing, but oversize the holes in the tube so you don’t have to get perfect alignment. This definitely requires adhesive in addition as the tube would be able to move the amount of the oversize holes, the bolts would basically be clamps.

[Chotu]

These decisions sometimes get harder and harder when new advice comes in. Whew!!

I can definitely see the point in the last couple posts. And weight is always the primary concern with this boat.

Dsanduril: the pultruded tubing I’m looking at is 3” x 3” x 1/4” wall thickness. That’s what’s required for the davits section according to all my math. The roof stiffening section needs much smaller stuff. A single thickness would look better, but at the same time it’s excess weight.

JebLostInSpace: You make GREAT points here. The boat is a looker in some ways, but I have a crowded cabin top/roof with all kinds of stuff up there. So maybe it’s ok to have the cabin top a little more utilitarian? More about business than looks? You don’t see the cabin top unless you physically climb up there and look around. Otherwise it’s not very visible at all from off the boat or on the boat.

[rslifkin]

I wonder... Do you have plans to put anything like solar panels on the cabin top? If so, the angle pieces might be better, as they could be used as mounting rails for things like that.

[pcmm]

Originally Posted by Chotu

I could continue the square tube of the davits all the way forward across the whole roof. I feel this would be visually appealing. EXCEPT I need to drill a bunch of holes in it for through bolting it. That would look awful and be difficult to do. It would look like Swiss cheese.

Why even through-bolt? Tap the holes and just thread in the fastenings or if you are worried about ultimate strength put some SS plates into the interior of the tubing and thread those.

[Chotu]

Originally Posted by pcmm

Why even through-bolt? Tap the holes and just thread in the fastenings or if you are worried about ultimate strength put some SS plates into the interior of the tubing and thread those.

Perfectly valid for the roof stiffening section. Probably not robust enough for davits section. Tubing is an FRP pultrusion.

[Chotu]

Originally Posted by rslifkin

I wonder... Do you have plans to put anything like solar panels on the cabin top? If so, the angle pieces might be better, as they could be used as mounting rails for things like that.

There is tons of crap up there. When you are doing a “no through hulls “ boat, that roof becomes essential.

Current roof inventory:

*Twin small air cooled generators
*Twin 15,000 BTU air conditioners
*700 watts solar on starboard side already installed, another 700 watts on port installed soonish.

** these stiffeners are between that solar and the generators and air conditioners.

It’s really a utility roof

Note: it says aluminum in the drawing. It’s FRP now

[pcmm]

Originally Posted by Chotu

Perfectly valid for the roof stiffening section. Probably not robust enough for davits section. Tubing is an FRP pultrusion.

If they are FRP then slide in a piece of 1/4 x whatever stainless that you have tapped. should work great then. Same as they do for installing trailer hitches on some cars.

[keyway]

If your tubing is 3x 3 it would not be to difficult to drop some elevator bolts down though the holes. For alignment I would make a template out of whatever is handy. It’s sealing under the tubing and holes is what would concern me

[joelhemington]

Originally Posted by Chotu

I was thinking of toggle bolts but was definitely concerned if they would be strong enough but also wondering if I’d be able to get the 25 holes to line up well doing it blind.

Looks wise, your idea is better than mine 100%

If I can pull it off...

The square tube would look better and theoretically be stronger. If your concern is lining up the bolt holes, just prefab the whole thing using a drill press for exact alignment of the holes. Doing this free hand is iffy at best. If you look at the wings of toggle bolts, you'll see that they're not terribly robust compared to through SS bolts. And do seal the ends if using the square tubing.