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Old 11-10-2019, 00:02   #1
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Autopilot shelf

I am constructing a shelf for the autopilot ram I am installing on the goat. I made a 3 sided shelf to extend from the hull out of 3/4 plywood. I have 1700 biaxial cloth. How many fiberglass layers should I put down to provide enough strength.

The bolts that came with the autopilot to mount it are good for thicknesses up to 24mm which is just under an inch.

I was going to apply some glass to the bottom side of the shelf before mounting it/ glassing it into the hull for better access. Prior to mounting I was going to put down some thickened epoxy to smooth any irregularities on the hull.

I was going to use 206 slow harder because it is hot here in Mexico. Should I try putting them all down at once? Or wait 20-30 mins between layers.

This is my first fiberglass project so I'm trying to plan it all out.
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Old 11-10-2019, 00:50   #2
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Re: Autopilot shelf

You’re more protecting the wood than adding strength, as 3/4 ply should hold up fine unless you’re doing a huge job. Yes to what you’ve suggested, plus put some very thickened epoxy in the corners as fillets. Once these have gone a bit firm, say a couple of hours, you can lay over the top. Do all the layers at once. Cut everything ready, then lay them on a sheet of plastic and soak them in epoxy layer by layer. Take the wetted pieces and drape them where they go, poking with a brush to remove all air bubbles. Use a fin roller when all the pieces are in place to remove as much epoxy as you can, to get the best strength. I’d recommend a sheet of peel ply over everything when done, rolled down. This will give you the best surface ready for paint.

Oops, didn’t answer your question. Three layers would be plenty.
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Old 11-10-2019, 06:04   #3
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Re: Autopilot shelf

I'm doing the steering on my f/g yacht and had to make up some "anchoring" lugs to take the steering pulleys I made up two 24 in. "e" shaped anchors using 30mm ss flat bar and fiber-glassed them to the hull each side of the quadrant.

I had a fair idea what to do but decided to contact the expert at the resin/glass distributors. The first question he asked was:
  • why are you using epoxy and not polyester? (But said to go ahead with epoxy as I had started)
  • Grind back the glass of the hull fairly heavily and ensure there are no dips and hollows.
  • Coarsely sand the ss flat bar both sides.
  • Use f/g cloth. Fold the cloth back over the tangs.
  • Do the whole lay-up within one day
I intend installing an autohelm and there is no way I will use ply.
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Old 11-10-2019, 07:58   #4
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Re: Autopilot shelf

Here is a picture of the shelf. It took me almost 3 days to build it due to patterning, shaping, and having to remove the old shelf that was too high.

I still need to sand the surface for prep to remove more of the paint.

With regards to the layers I want the top to be flat so I was going to use cloth that was bigger than that surface and drape over the sides. For the sides I was going to tab it in using thinner pieces, but they will overlap Causing uneveness.

On the bottom,. Going to add glass to the bottom before installing and leaving the piece exposed about 2 inches. I was then going to install with thickened epoxy, but I'm concerned the glass I put on the bottom will already be dry and not able to accept new glass. It is very hot here during the day so I'm concerned regarding working time especially since this is my first glass project.

The long front piece is open so I have access to the bottom to glass/tab it in.

I'm also planning to add a metal backing plate onto the backside when I bolt down the autopilot.
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Old 11-10-2019, 08:06   #5
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Re: Autopilot shelf

Is that a Tartan 37 by chance?
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Old 11-10-2019, 08:15   #6
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Re: Autopilot shelf

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Is that a Tartan 37 by chance?
Yes 1980 Tartan 37. The ram was too long to fit perpendicular to the boat. I rotated it slightly to keep things perpendicular to the rudder post and provide the appropriate height for the connection to the arm.
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Old 11-10-2019, 08:53   #7
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Re: Autopilot shelf

Thought I recognized it, had one for 20 years. Love the boat. Are you familiar with the Tartan 37 website?
Tartan37.com
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Old 11-10-2019, 09:06   #8
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Re: Autopilot shelf

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Thought I recognized it, had one for 20 years. Love the boat. Are you familiar with the Tartan 37 website?
Tartan37.com
Yes. I post there all the time.
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Old 11-10-2019, 09:13   #9
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Re: Autopilot shelf

Watchout... the rams require way stronger mounts than you'd think.

Designs for a Strong Autopilot Drive Mount / Shelf?

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Old 11-10-2019, 13:45   #10
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Re: Autopilot shelf

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Originally Posted by funjohnson View Post
Watchout... the rams require way stronger mounts than you'd think.



Designs for a Strong Autopilot Drive Mount / Shelf?



Matt


The loads on the shelf can be surprisingly high. I would take particular care to filet and layer a number of layers of biaxial cloth to tie it into the hull. This is an area that more robust attachment is better.

A few years ago a boat came into Papeete that had their hydraulic AP ram mount ripped off the hull due to light attachment points.

Good luck

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Old 11-10-2019, 15:14   #11
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Re: Autopilot shelf

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Originally Posted by chouliha View Post
The loads on the shelf can be surprisingly high. I would take particular care to filet and layer a number of layers of biaxial cloth to tie it into the hull. This is an area that more robust attachment is better.

A few years ago a boat came into Papeete that had their hydraulic AP ram mount ripped off the hull due to light attachment points.

Good luck

Chuck
This. My recommendation would be to take your existing design to a metal fabricator and have them weld one using SS. Youíre in Mexico. Work is cheap and there are SS welders servicing every marina.
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Old 11-10-2019, 15:37   #12
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Re: Autopilot shelf

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Originally Posted by Tillsbury View Post
Youíre more protecting the wood than adding strength, as 3/4 ply should hold up fine unless youíre doing a huge job. Yes to what youíve suggested, plus put some very thickened epoxy in the corners as fillets. Once these have gone a bit firm, say a couple of hours, you can lay over the top. Do all the layers at once. Cut everything ready, then lay them on a sheet of plastic and soak them in epoxy layer by layer. Take the wetted pieces and drape them where they go, poking with a brush to remove all air bubbles. Use a fin roller when all the pieces are in place to remove as much epoxy as you can, to get the best strength. Iíd recommend a sheet of peel ply over everything when done, rolled down. This will give you the best surface ready for paint.

Oops, didnít answer your question. Three layers would be plenty.
Agree with this, but you don't really need to wait for the fillets to cure, or even part cure.

"Wet on wet" glassing over fillets produces excellent results.
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Old 11-10-2019, 16:58   #13
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Re: Autopilot shelf

Well I agree with Matt, Chuck and Chouliha's approach.

I'm going to heavily glass SS anchor points to the hull and then make up a "box" using SS angle to take the forces of the ram.

I did use the link to the CF thread on auto-helm installation but I don't think ply is the way to go.

https://www.google.com/search?client...UTcCK4Q4dUDCAY
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Old 11-10-2019, 17:46   #14
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Re: Autopilot shelf

You do not say which autopilot drive you are using. How much force can it develop?

I disagree with the idea of epoxying SS anchor points to the hull and then attaching to those anchor points. That is point loading the stress. Spread the load out by fiberglassing the entire shelf to the hull. Don't let the length of supplied bolts limit your mounting options. That is false economy. Bolts are not expensive. Use a double thickness of 3/4 plywood. Consdider that the shelf spaced away from the hull will apply a twisting force to the bracket (shelf). Also consider reinforcing the inside of the shelf with plywood along the lines of the force.

My solution, almost 30 years ago, was to make a flat topped pyramid of plywood 1.5 inches thick. The bolts heads are recessed into the base of the pyramid and the bolts extend through the top where the autopilot drive bracket is held on with nylock nuts. The pyramid is fully encased in fiberglass and attached to the hull with four layers of cloth. The pyramid shape distributes the load over a wider area of the transom. This was for an Autohelm (now Raymarine) type 2 linear drive. That was done in 1991 and 130,000+ miles later it is still as good as the day it was done.

The previous owner had reinforced the transom with a few layers of cloth and through bolted the bracket. I couldn't stand the sight of the bolts so I did the glassed in pyramid.

PS. This is on a 44 foot, 24,000 pound boat.
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Old 11-10-2019, 18:32   #15
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Re: Autopilot shelf

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You do not say which autopilot drive you are using. How much force can it develop?

I disagree with the idea of epoxying SS anchor points to the hull and then attaching to those anchor points. That is point loading the stress. Spread the load out by fiberglassing the entire shelf to the hull. Don't let the length of supplied bolts limit your mounting options. That is false economy. Bolts are not expensive. Use a double thickness of 3/4 plywood. Consdider that the shelf spaced away from the hull will apply a twisting force to the bracket (shelf). Also consider reinforcing the inside of the shelf with plywood along the lines of the force.

My solution, almost 30 years ago, was to make a flat topped pyramid of plywood 1.5 inches thick. The bolts heads are recessed into the base of the pyramid and the bolts extend through the top where the autopilot drive bracket is held on with nylock nuts. The pyramid is fully encased in fiberglass and attached to the hull with four layers of cloth. The pyramid shape distributes the load over a wider area of the transom. This was for an Autohelm (now Raymarine) type 2 linear drive. That was done in 1991 and 130,000+ miles later it is still as good as the day it was done.

The previous owner had reinforced the transom with a few layers of cloth and through bolted the bracket. I couldn't stand the sight of the bolts so I did the glassed in pyramid.

PS. This is on a 44 foot, 24,000 pound boat.

It is not just a matter of how much force the ram can develop: what about forces on the rudder!

In regard to your second point I refer you back to the third comment on the thread. The two anchors are made up of 24 inch 1.5 inch SS flat bar with three 6 in.tangs welded to each. (I fiber-glassed it to the hull with advice from a fiber-glassing expert) Please refer to the photo.

It is probably an overkill but I will join each anchor by bolting SS angle from one anchor (under the quadrant) to the other.
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