Forestay bridle fitting

I had a similar discussion a few years ago, when I added a forestay fitting to the flimsy A-cat hull for my foiler build. I chosed a bulkhead design then, but it is not suitable here.

This time it is the Nacra 5.8 hull for my trimaran. They have heavily built gunnels that can withstand the upward forces. I can as well use a bridle, as the Tornado jib will have its tack at least 40cm above deck. Will go for Dyneema rigging.

I have prepared the hull for the G10 block and begun shaping it for a good fit and will of course use thickened epoxy to fix it.

I have sketched three versions, but I am not so keen on the left one and like the right one as it keeps the hull sides apart and the deck free. In the lower right image an original chainplate can be seen.

Which one of the two remaining should I go for, or is there maybe an even simpler(and better) way of doing it?

 

The simplest way is to just have the jib fastened to the existing chainplate, it doesn't matter if it's offset. Your solution with the big bolt looks good to me.

 

Also thought of the simplest solution, but got second thoughts about the strength of the single chainplate. Offset would only be ca 1 degree in relation to hull length,

About the bolt I did a simple loadcase with 304 10x1mm tubing and 6kN forestay load and that should just about do it. The M8 threaded rod inside will give an added safety factor. Not to heavy either at below 150gr including nuts and washers. Untraditional but slim.

 

I can understand your fears, even if the chainplate did held up a mast in its previous life.
I wouldn't muck around with any tube, use M12 threaded rod (plain bar threaded only at the ends would be better), big washer and nut on the inside, big washer and nut on the outside, thimble to fit over the nut, another washer and nut to secure the thimble. For low cost, galvanized allthread, paint with epoxy followed by regular paint. Disassembly is with the help of a heatgun.

 

I like the thru bolt/rod method.

I did something kind of similar to repair the bridle anchor point on the Starboard hull bow of my Hobie Wave.

The Port side of the bridle failed leaving only the center and Starboard side to keep the mast standing while the boat was fully powered up, and the Starboard bridle pad eye and anchor ripped right out of the plastic hull.

I called Hobie to find out how the bows were constructed to figure out best fix, and they refused to help saying the hull was junk and needed to be replaced. Right, just what we need, an otherwise functional plastic hull tossed in our dump.

In the end, I hand fabricated a Stainless nose that curved over the bow tip attached with two thru hull cross bolts and mechanically bonded with 3M 5200 with the pad eye then anchored in its original location.

Being a plastic boat there weren’t a lot of options.

I just knew that I didn’t want to have to worry about it ever failing again.

That was many years and many fast and hard sailing sessions ago and it’s been holding up perfectly. Just had it out a few weeks ago in 30+ and I pretty much always push the boat hard wether it be sailing fast, surfing waves or launching off swell. Only drawback is a bit more spray from that hull, but there’s no escaping getting wet on this boat as you can see from video.

I laugh every time I think about the guy at Hobie that told me there was no way to repair it and that the hull needed replacement when all I wanted to know was if the bows were hollow or solid in that area.

BTW, the real reason for the failure was due to dissimilar corrosion as whatever Hobie had used as captive impregnated nuts in the hull when it was manufactured had turned to power inside due to ingress of salt water and mix metals used to make up the bridle anchor.

Not shown in the last photo but seen in the video is the addition of a center forestay extension that runs all the way down to the crossbar to which the Jib clips for better sail shape, but also to act as a backup incase one bridle side ever fails again.

 

What a story. Great fix. Like the film, fun sailing. Would rather sail that one than a H14.

Will not go for tube or threaded rod. Will instead thread a 10mm 1.4301 rod in both ends and lock the rod with nuts and West G/Flex 655.

The loadcase says ca 300MPa stress for a rod without nuts at the ends. With nuts and epoxy added, stress will be even lower. 1.4301/304 has a maximum stress of at least 500MPa.

EDIT:
The side force from the bridle will not be more than 0.8kN from each hull side so the rod is not necessary for compression reasons. Could as well simplify and use two short M10 bolts with shank. Same, same but different.

 

There ya go, even better. Helps to have access!

I’m always preaching about how much fun and what a bang for your buck the Hobie Waves are.

Most people write them off as a beginners slow poke boat, and they definitely aren’t as fun as an old school H14 out of the box, but with a few modifications and some tuning skills, they are a blast to sail single hand, and the high volume plastic hulls are awesome in swell as they absorb a lot of the impact when launched off which they tend to do as opposed to slicing through like the old fiberglass big rocker low volume hulls.

And when you set them up just right for the conditions, although still a handful, they are predictable and easy to control with minor weight shifting and sail trimming, and so simple without any boards, excessive control lines, hiking out crap, etc..

For the money they sell for used, I don’t think there is a more simple, (mostly) indestructible, fast and fun single hand beach cat that can also be loaded up with people and cruised around when desired without looking like it’s half sunk like the classic Hobies.

Anyway to get them into hot rod/sports car form they need a jib, the forestay lengthened so you can rake the mast back to shift CE and keep the bows up, the tillers cut down so you can sit as far back as possible, and a 6:1 mainsheet setup.

I also added these handy little adjustable cam buckles that make quick work of adjusting the mast rake and tensioning the rig as the conditions change throughout the day. I mention them because they may be of interest to you or others.

I almost bought another Wave for $100 the other day that was missing the rig because I felt sorry for it! Also because I think they would make a great little tender.

Okay, enough preaching… back to your Tri build which I’ve been enjoying seeing come along as I may someday need to build something similar with all the parts I’ve collected and project boats that somehow find their way to me, but more importantly as I get older and desire to continue to sail fast but flatter.

 

Have actually a simpler version of the same type from RWO. Have one at the forestay on a dinghy to loosen rig tension after sailing. Great gadget. About trimaran and flatter sailing the ideas came to me after I turned 70 a while ago, after being a cat and dinghy guy all of my life .

 

Sketch and realization. On the inside is a bent ca 2.5mm stainless steel plate, reinforced to 5mm where the hole for the 10mm bolt is.