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Davit attachment points?


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My S11N is steadily progressing. Before I get on to the finishing stage, I should give some thought to how I am going to carry it on davits.

I expect to use the davits primarily to keep it out of the water at night, and perhaps on shorter passages in good weather. I think it's going to be a bit big to safely hang off the yacht in rougher conditions.

 

I would like to have it secure in the davits, so it is not rocking around at all. That means attachment points low down in the boat allowing me to haul it up tight against the davit arms (with appropriate fendering, of course). The loads could be fairly high doing it this way.

 

I'm wondering about fitting strong points on the front face of each aft seat compartment, and another perhaps on the forward end of the centreboard case. Does that sound reasonable? I don't want to reinvent the wheel, presumably somebody has thought of this already...

 

If it helps, the davits are not yet fitted to the boat, so the exact distance between them could be chosen to suit the dinghy.

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8 hours ago, Aphers said:

The loads could be fairly high doing it this way.

I think that is an understatement.  Will you be using a winch?

 

I would definitely consider some kind of build up as the base of your lifting points, to spread the load out. I don't think anything about the boat is prepared for such loads.

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Thanks, you're right, the loads will be significant. I could probably get away without a winch, maybe a 2:1 purchase would be enough. I would probably want to set up the lifting lines in a way that there was a stopper to prevent over tightening.

 

I thought about bolting an eye right through the keel, that would be about as strong as you could get. But unless this is next to a bulkhead, it's going to be putting a lot of compression strain on the hull.

I'm thinking that the mast step might make a suitable attachment point? As designed it isn't through-bolted of course, so it would need to be modified.

 

Further aft there isn't such an obvious place. Maybe just an eye bolt on the floor about half way along the length of the seating. Or right at the bottom of the transom and accept that it will be pulling at a bit of an angle.

 

Would be interested to see what other people have done?

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Very happy to see this post. I have just started the build of a Spindrift 11' standard.

I plan to hang her on davits and have been wondering where to put the attachment points.

I worry about bolting through the buoyancy tanks because I think the bolts will move over time and leak. One thought is to glass blocks of wood with the attachment eye in place. I would recess the nut so the blocks would fit flat.  The attachment points on my inflatable are hypalon  patches that are glued on and holding well. 

Looking forward to more ideas from the group.

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There are as many ways to mount hoisting hardware as there are different davits.

 

A S11 needs a good size sail boat to be able to use davits. I like to use a 3 point attachment so that the boat will not tip over. The CG is well above the bottom. I am showing a 5' 4" attachment length in the renders, this lets you mount a pair Harken 1558 eyes trap on the forward end of the aft flotation tanks P & S. You can add a couple of 6mm ply backing pads on the inside, fillet and glass them well inside and out. The forward end shows a H 137 eye strap bolting through the keel.  These eye straps take 1/4" fasteners. 

 

It is certainly a lot easier to build if you make these decisions before you put lids on the tanks.

 

You better have open drains if the boat is going to hang in davits. One good shower could tear up the deck or break the davits.

S11n hoist1.jpg

S11n hoist2.jpg

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Graham I'm building the 11' non nesting. I was planning to leave the back open and have the tanks die straight into the transom. I thought this would leave a clear path for a drain hole in the transom. This will allow the dinghy to tilt lower in the back and drain. Because the tanks go all the way to the forward bulkhead should I still use the measurements you gave for the 11' nesting  model ?  You say to put a good backing plate inside the tank. Would you through bolt and then glass over the nut to keep it from ever leaking. Before the seat covers are put down.

I have a 38' Osmond Beal downeast style lobster yacht so lots of room for the Spindrift.

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Thanks Graham, that's perfect. Similar to what I had first thought of, although I had considered using the front face of the aft seats. Another thought was to add rubbing strakes near the chine, and through bolt to those, to help spread the load over a bigger area.

My yacht is 39ft and 13'10" in the beam, any smaller and the 11ft Spindrift would look pretty silly up there.

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Tim,

 

A  S11 should look good on a Beale 38. Those dimensions for the nesting version should work pretty well on the standard S11. It also depends on the davit spacing. I just based the length on the for end of the aft tank with room for fasteners at the forward end of the keel from midships. You could add another pair of H1558's on the forward end of the side tanks so that you could have any davit spacing that would work for your Beale.

 

Aphers, The same goes for you in terms of davit spacing. You could do as you suggested and add some reinforcing at the chine forward on the inside and bolt on a pair of H1558's

 

I don't know if either of you are going to sail your Spindrifts. I consider an Anderson bailer to be indispensable on them which works out perfectly for draining as you can trim the boat out level on the davits and the bailer will be at the low point except for the nestor, it will need 2.

 

I like davits when they will work. While crossing the Mediterranean we enjoyed the company of crew on a 45' steel boat off and on. I once said " do you ever worry about the dinghy in the davits on an ocean crossing?" He said " everyone asks me that, ever since we left Australia, but her we are." We left Gibraltar on the same Levanter (east wind). We fetched up with them later in the Canaries. The dinghy was gone and the davits looked like pretzels. They got caught in the same Winter north Atlantic storm as we did.

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Graham, thanks for that. My own anecdote about the dangers of davits is that a large yacht local to me got caught out in heavy weather. Their console RIB complete with outboard ended up swinging by one strap, sweeping the cockpit at head height. It took a very well timed scramble up the davits to cut it free. Terrifying.

 

We only plan to use the davits for overnight storage and shorter day sails- if we thought it was a viable permanent option we wouldn't have chosen the nesting dinghy.

 

We do indeed intend to sail her. I have an old ex-club dinghy that I am stripping parts from, so I already have the two Andersen bailers that I'll need, along with rudder fittings, cleats, blocks, etc.

 

 

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Yes the plan is to sail the Spindrift. No plans to be caught out in the conditions you both talked about. Been there done that. We carried an Avon roll up lashed on deck on our sail boats. Lost a dink off a painter once and that was one too many.

Want to enjoy the quaint little harbors of Maine sailing around in the "tender".

 

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In my post above, I mentioned that I was considering adding bilge strakes- primarily to reduce wear and tear on the bottom of the boat. Well tonight watching Sailing Florence, I spotted that their S9N has these. Theirs are pretty long, reaching the transom, and are further inboard (closer to the keel) than I had envisaged.

 

I like the idea of through-bolting into these strakes to create the aft lifting eyes- the load would be spread right across the bottom of the boat. I'll probably use something like 19x19mm ash for the strakes.

 

This would probably put the rear davit eyes slightly further aft than Graham showed, maybe around 12 to 18 inches, assuming I want the eyes coming through next to the aft seating. Or I could move the strakes further away from the keel.

 

I am planning to use a small Bison trolling motor on the boat and that extra weight on the transom concerns me.  Moving the lifting points slightly aft feels like the right thing to do... although I don't want to put extra stress on the nesting joint. I suppose it's a trade-off. And I guess the forward eye would have to move a similar distance forward.

 

Would be interested to hear any thoughts on this plan.

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Aphers,

Looking at Graham's picture he has the pick-up lines straight above the pick-up points. I'm thinking

the attachments are drawn at the balance points.

It seems to me if you spread the pick-up points so the angle of the pick-up line is a bit aft of straight down and a bit forward of straight down as you lifted the boat it would try to pull the boat together. Maybe not be a lot of force but should help any shear on the bolts holding the two halves. I'm not an engineer but but I play one on day time tv.

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1 hour ago, Captain Tim said:

Aphers,

Looking at Graham's picture he has the pick-up lines straight above the pick-up points. I'm thinking

the attachments are drawn at the balance points.

It seems to me if you spread the pick-up points so the angle of the pick-up line is a bit aft of straight down and a bit forward of straight down as you lifted the boat it would try to pull the boat together. Maybe not be a lot of force but should help any shear on the bolts holding the two halves. I'm not an engineer but but I play one on day time tv.

I see what you're saying but doesn't that depend upon the distance between the davits? I've not fitted mine yet so I can have them further apart than on Graham's drawing.

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Yes the placement of the davit plays into it.

I thought you have not fixed your davits to the mother ship yet.

Another advantage of angling the pick -up line might be that it slows down the swing of the dinghy when using opposing tie downs. ( remember my day time job)

 

 

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If the davits are closer together than the pick ups, then it will force the top bolts connections together, but try to pull the bottom hardware connections apart. And then there is the reverse. A little of either may not be a big deal.

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33 minutes ago, Hirilonde said:

If the davits are closer together than the pick ups, then it will force the top bolts connections together, but try to pull the bottom hardware connections apart. And then there is the reverse. A little of either may not be a big deal.

Also the lifting points are down on the floor, so perhaps the force on the bulkhead is mostly compression... I think... but I am an not an engineer and don't even play one on TV (although I do work on and drive boats for a living...)

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