Folding Pad Eye for Gennaker Block Mounting

[hoppy]

Is a folding pad eye with a breaking load of 4400kg sufficient for mounting a gennaker/code zero sheet block?

I bought the pad eye originally for the jack lines but now I am wondering whether to install them in a position when they can be used for a gennaker (whenever I get one).

I am guessing that 4400kg is more than enough, but I figure it is better to find out for sure before I drill some hole

The boat is 40ft and in the manual the spinnaker size is 108sqm and I guess the gennaker would be a little less.

[witzgall]

We have a double wichard padeye for a storm sail mounting point. I have seen others use the same, so I would go for a big double.

Chris

[islandplanet]

Hoppy,

I'd want to know the safe working load rather than the breaking strength before commenting.

[hoppy]

I noticed that most blocks and other things I looked at quoted both breaking and safe working loads, but the pad eye only had breaking. Do you know how much safe working load is needed?

[beetle]

You might talk with your sailmaker and ask them what they expect the tack loads to be on that sail, and add your own safety factor.

Alternatively, you might assume the load will be equivalent to the halyard sheave or block load and select a padeye accordingly. 4400kg break load seems low to me for handling shock loads; for example, Harken specifies padeye working loads at roughly 1/2 breaking load.

- rob/beetle

[Doodles]

If I'm reading this right it looks like the working load (funct. ?) is about 55-66% of the breaking. Also, interesting that the single padeye loads are the same as the double? Am I missing something or else why spend the extra on the double. Maybe on the double it is per eye?

Wichard Pad Eyes

[daddle]

Does the sheet turn 180 at the block? That would double the load.

[beetle]

Originally Posted by daddle

Does the sheet turn 180 at the block? That would double the load.

The tack line would normally turn 90-100 degrees at the tack padeye, assuming the tack line is adjustable from the cockpit, and that turn increases the load seen at the padeye by 1.4.

A 180 degree turn is more likely seen by things such as genoa sheet and spinnaker sheet turning blocks, as well as main and jib halyard sheaves.

- rob/beetle

[daddle]

Originally Posted by beetle

The tack line would normally turn 90-100 degrees at the tack padeye, assuming the tack line is adjustable from the cockpit, and that turn increases the load seen at the padeye by 1.4.

A 180 degree turn is more likely seen by things such as genoa sheet and spinnaker sheet turning blocks, as well as main and jib halyard sheaves.

- rob/beetle

OP wrote "sheet"

[beetle]

Originally Posted by daddle

OP wrote "sheet"

Oops! - quite right. Then the load may double.

[islandplanet]

Load will be dependent on a lot of factors:
Sail size
Sail material (nylon absorbs some loads)
Wind
Tenderness or stiffness of boat (this is why cat sails are so heavily loaded - the boat doesn't heel)

You mentioned your spinnaker is 108m and that you expect the gennaker to be smaller which is true. If we were selecting a foil-less furler for the boat we'd probably be looking at something with at least 3500lb working load.

You may want to consult a rigger for advice on which fitting to procure.

[Palarran]

I'm going to do the same thing for my spinnaker tack point on each pontoon near the tip. The wichard pad eye that I ordered has a working load of 2400kg and a breaking load of 4500kg. The tack line is 14mm and looking at charts, it's tensile strength isn't far off the working load. The boat has the same pad eyes right now for the spin sheet block.

I'm wondering two things;
1- Do you think these pad eyes are strong enough for a spinnaker tack point - no idea of the sail size, but it's pretty big.

and
2- What kind of backing plate do you use? Should I use a solid piece of aluminum? Do you bed this backing plate into fiberglass if the surface isn't completely flat? I'm less worried about the pad eye breaking as the fiberglass structure pulling apart.

[UNCIVILIZED]

Realistically, for a mounting point for a spin sheet on a 40' cruiser, a 2,000 - 2,500kg working load is enough. Assuming that is that you douse the kite by the time the winds get up to 20kts/20kts+. It's going to need a good backing plate though, & to be mounted in an area where there's enough structure to carry a lot of load.

Some of this is experience based, & some's simple math. Since if you have a 125sqm kite, & it's blowing 20kts, the sheet load will be around 1,200kg (in theory, less in practice). You can work out the math here Harken Sailboat Hardware and Accessories

The one catch though is that you need to align the padeye so that it's properly oriented to optimally take the load. As the rated load for any padeye differs depending on the angle of pull that it's subject to. So if in doubt, you can't really go too big, particularly if you don't know at what angle the BL or SWL was calculated & tested at.

Originally Posted by Palarran

I'm going to do the same thing for my spinnaker tack point on each pontoon near the tip. The wichard pad eye that I ordered has a working load of 2400kg and a breaking load of 4500kg. The tack line is 14mm and looking at charts, it's tensile strength isn't far off the working load. The boat has the same pad eyes right now for the spin sheet block.

I'm wondering two things;
1- Do you think these pad eyes are strong enough for a spinnaker tack point - no idea of the sail size, but it's pretty big.

and
2- What kind of backing plate do you use? Should I use a solid piece of aluminum? Do you bed this backing plate into fiberglass if the surface isn't completely flat? I'm less worried about the pad eye breaking as the fiberglass structure pulling apart.

For a tack padeye on a Code 0 personally I'd want something stronger. As even with zero wind in the sail you'll be putting quite a lot of load onto the halyard, & thus the padeye, particularly if it's a 2:1 halyard. And then you have to add in the loads created by the wind in the sail. Ergo, go up a size or two.

For backing, aluminium, G-10, FRP plate, or stainless works. Though if there's any concern about the strength of the deck in that region you'll want to;
- make sure the laminate's not cored
- add some extra glass to the deck's underside, possibly tying things into the hull with reinforcements. And or, also adding knees or ring frames. The latter are KISS to install, & pretty dang effective.
- at a minimum bed the backing plate in structural bog (epoxy mixed with chopped or milled glass fibers). And bonding a G-10 or FRP plate (aluminum too) in place with bog would be preferable, as this will help spread out the load even better, by tying the backing plate into the deck's structure. Thus strengthening it.
- Also, bevel the edges of any backing plates. It reduces the stress risers at their edges (point loadings).

Bottom line on all of these questions though is if in doubt, go up a size. As the extra $20-$30 that you spend on the larger padeye is cheap compared to 99% of everything else onboard. And you can't even by a date/the Mrs. dinner at a resturant for that, so...

[Palarran]

The pad eye I ordered is the largest Wichard makes. Also, this isn't for a code 0 but a standard Asym. While winds can get strong quickly, we always douse the spinnaker when the apparent wind exceeds 16 knots. This doesn't affect the boat much as my main and jib will propel me as fast in winds this speed anyway.

I wish I knew the sail sf so I could use that calculator. Though as I said, we have been using the same pad eye for the spin sheet since purchased. Also, the prodder currently uses two mounted on the hull low in order to support it. Probably the loads are 80/20 on those, so it's not much different.

Good advice on the backing plate. That is what I mostly was thinking.

[Palarran]

Actually, after looking at that Harken calculator, the better one would be main sheet load. For my main, it's approximately 1224 kilos at 16 knots.

Harken Sailboat Hardware and Accessories