Davit Hardware...
 

... I have a set of cast Danforth Davits. Have blasted and painted them
and am now nearly ready to put them on the boat.

They are rated 175 lbs each.

They are going on the stern of a 39' 1980 center cockpit boat. The
fiberglass is very thick.

First, I'd like your collective input on how much/what sort of bracing
in the aft cabin to support the davits with a hardshell dinghy mounted.
I'm thinking a piece of 1/2" aluminum - to cover the space between the
davits plus 4-5" wider all round.

Second, what quantity (blocks) and other type of hardware will I need?
What size line will I need? This will determine the type of block.

Sorry to sound so dense but I'm relatively new at this and there is
no-one around here to ask. (I'm the only sailboat at the yard (all rest
are fishermen or shrimpers).

Thirdly, I've got to balance effort against price. I don't think I can
afford an electric hoist, nor do I see where it could be mounted, so a
hand winch will have to do. So, how do you get two hoist lines to go on
one winch? (I'm guessing it's a matter of more pulleys(?)

TIA

--
Molesworth

Davit Hardware...
 

Molesworth wrote:
.. I have a set of cast Danforth Davits. Have blasted and painted them
and am now nearly ready to put them on the boat.

They are rated 175 lbs each.

They are going on the stern of a 39' 1980 center cockpit boat. The
fiberglass is very thick.

First, I'd like your collective input on how much/what sort of bracing
in the aft cabin to support the davits with a hardshell dinghy mounted.
I'm thinking a piece of 1/2" aluminum - to cover the space between the
davits plus 4-5" wider all round.

My rough rule of thumb for backing plates = 0.5 x fastener diameter.
1/2" is way overkill. No need to span between the davits, the middle
part of the backing plate won't be doing anything for you. Just a few
inches bigger in both directions than each davit pad.

Second, what quantity (blocks) and other type of hardware will I need?
What size line will I need? This will determine the type of block.

I'd use a 4:1 purchase at each end. Fiddle blocks. If your dinghy
weighs 100 lbs, then each purchase lifts 50 lbs. 50 lbs/4 = 12.5 lbs
so very easy to pull by hand. Use 5/16" line because 1/4" is a bit
hard on your hands. Make sure the top block has a built in cam cleat
if your davits don't have their own cleat.

Sorry to sound so dense but I'm relatively new at this and there is
no-one around here to ask. (I'm the only sailboat at the yard (all rest
are fishermen or shrimpers).

Thirdly, I've got to balance effort against price. I don't think I can
afford an electric hoist, nor do I see where it could be mounted, so a
hand winch will have to do. So, how do you get two hoist lines to go on
one winch? (I'm guessing it's a matter of more pulleys(?)

With difficulty. Easy way is to have 2 independent drums on same
shaft. How heavy is your dinghy?? Two tackles are a lot simpler.

Evan Gatehouse

Davit Hardware...
 

Molesworth wrote:
.. I have a set of cast Danforth Davits. Have blasted and painted
them
and am now nearly ready to put them on the boat.

They are rated 175 lbs each.

They are going on the stern of a 39' 1980 center cockpit boat. The
fiberglass is very thick.

First, I'd like your collective input on how much/what sort of
bracing
in the aft cabin to support the davits with a hardshell dinghy
mounted.

First things first.

If you take a wave over the stern with the dinghy in place, 175#
rating/bracket will hopefully be the failure point and not tear your
stern out.

Your problem is stress concentraation where the fastners attach the
brackets to the hull.

Use some 15# urethane foam against the inside of the hull formed to
match the hull, then bond in place with SikaFlex 291.

Glass foam to hull after SikaFlex cures with some epoxy and double
bias glass, then use a 1/4" S/S plate(s) to distribute the stress at
the fastener penetrations..

SFWIW, I'd sell the davit brackets and keep the dinghy on deck.

Lew

Davit Hardware...
 

In article ,
"Lew Hodgett" wrote:

Molesworth wrote:
.. I have a set of cast Danforth Davits. Have blasted and painted
them
and am now nearly ready to put them on the boat.

They are rated 175 lbs each.

They are going on the stern of a 39' 1980 center cockpit boat. The
fiberglass is very thick.

First, I'd like your collective input on how much/what sort of
bracing
in the aft cabin to support the davits with a hardshell dinghy
mounted.


SFWIW, I'd sell the davit brackets and keep the dinghy on deck.

Lew

Thanks Lew. I take your point, and indeed the dink is currently on the
deck, but my problem is - I can't lift it on my own!

Maybe I'm approaching this problem the wrong way. St Croix plus
inflatable?

As I draw over 5', I have to have auxillary transport to get ashore in
shallow waters.

--
Molesworth

Davit Hardware...
 

"Molesworth" wrote:

Thanks Lew. I take your point, and indeed the dink is currently on
the
deck, but my problem is - I can't lift it on my own!

Have you tried to rig a halyard along with either the boom or a pole?

Lew

Davit Hardware...
 

In article ,
"Lew Hodgett" wrote:

"Molesworth" wrote:

Thanks Lew. I take your point, and indeed the dink is currently on
the
deck, but my problem is - I can't lift it on my own!

Have you tried to rig a halyard along with either the boom or a pole?

Lew

Lew,

Yes. The way we got it on board was a halyard from the mast top.. and
its sitting on some old quilts to prevent rubbing etc. Looks awful.

--
Molesworth

Davit Hardware...
 

"Molesworth" wrote


Lew,

Yes. The way we got it on board was a halyard from the mast top.. and
its sitting on some old quilts to prevent rubbing etc. Looks awful.

If you decide to use these davits, a suggestion:

Make the fasteners the weakest part of the design.

At least when they fail, they won't damage the transom.

Lew

Davit Hardware...
 

First off, how heavy is your dinghy and where do you plan to sail? The
davits that most people put on their boats are way too small for the shock
loads generated by pounding through seas and you'll end up bending them.
Personally I think that you need davits which are rated at 4x the actual
weight of the dinghy if you expect to have them survive in rough seas.

I use Atkins and Hoyle (http://www.atkinshoyle.com/) davits and have been
quite happy with them. I started out with their model 1800 davits, which
are rated for 180 lbs/davit, and I found that they weren't sufficient in
big seas. I then upgraded to their model 5000, which are rated for 500
lbs/davit or 750 lbs/pair, and these have been rock solid. Note that I
only lift a 120 lb dinghy without a motor.

Pay close attention to securing the dinghy to keep it from swinging from
side to side. I use SS coated cables which crisscross, from the bow
lifting point and the D-ring on the dinghy transom, to the opposite davit.
I also have a SS cable which goes from the other transom D-ring, which is
closest to the big-boat, up to the davit arm. All of the SS cables have
turnbuckles to tighten them and carabiners on the ends. It's taken me a
long time to come up with this solution, but the dingy remains solid even
in big seas.


-- Geoff
www.GeoffSchultz.org

Davit Hardware...
 

I got a couple of messages asking me about my davit setup, so I guess that
I didn't do a very good job describing it. So, here's a better description
and pointers to images which may provide more information than my verbal
description:

------------

The only photos that I have of the davit system don't reflect the current
setup, but between the old photos and some text, you can get the idea of
what I've done. I posted some photos online at
http://www.geoffschultz.org/BlueJacket/Davits/

As you can see, there's a Y shaped cable that connects the bow attachment
point to the transom D-rings. I had to do this because the tubes overhung
the bow attachment point and I couldn't get a clean lift. This Y cable has
a turnbuckle that adjusts the length to allow it to be removed/tightened.
The stern is lifted by a V shaped cable which connects to the transom D
rings.

While not shown in the photos, side to side stability is maintained by a SS
cable going from the bow attachment point to an eye-bolt on the starboard
davit. The eye-bolt is mounted right under the davit cleat. Another SS
cable goes from the dinghy's port transom D-ring to the an eye-bolt on the
port davit. These cables also have turnbuckles to tighten them. I used to
use line instead of the SS cables, but I found that the line
slipped/stretched.

Finally, a SS cable with turnbuckle attaches to the dinghy's starboard
transom D-ring and goes up to an eye-bolt which is mounted on the davit
arm. This is the part labeled "Davit Attachment Point" in the photos and
it clamps around the davit arm. You can see an early version of this in
the photo labeled "Dinghy Stern" which shows a line tied to the D-ring and
running up to a block with a cam-cleat. This keeps the dinghy from rolling
as the forward-starboard tube rests against the davit arm.

-- Geoff
www.GeoffSchultz.org