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Discussion Starter #1
I am considering mounting a Seaview 8 foot radar mast on the aft deck of my Columbia 45 inboard of the pushpit and anchored to the tubing with the fittings to the top rail. The pole is reported to be 3" O.D. aluminum and I'm concerned with it's ability to support the weight of the stainless arm of the Gahauer lifting tackle and the outboard without bending or flexing if the lifting arm pintles are mounted high enough to clear the pulpit and life lines. They offer a 48' support strut for the pole but it would mean additional fittings and deck or toe rail space. It would be ideal to mount an enclosed radome and cockpit floodlight as well.
My last Columbia had a 4" steel radar pole glassed through the aft deck and fixed to a glassed in wooden shelf on the hull interior. Bulletproof but heavy and expensive to build.
 

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Well, it will always bend and flex a bit. That is unavoidable. I suspect that a 3" OD pipe will be OK. What is the ID of that pipe?
 

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It also depends how big your outboard is!

Sent from my SM-G960W using Tapatalk
 

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I would contact the manufacturers of the radar mast & ask them.

A 6hp Tohatsu 4 stroke outboard is probably in the 50-60 pound range. They will need to know that.
They will also need to know the length of the arm that you plan to mount on the side of their mast.

If you want to guestimate the strength of a 3" tube yourself, you will need to know it's wall thickness.
 

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Discussion Starter #5
Thanks to all for your input and suggestions. I'll contact Seaview for wall thickness of their masts. There is a 4" mast as well that may be more appropriate since the Stainless Garhuaer lifting arm and tackle are approximately 35 lbs.
I would expect a number of cruisers with high freeboard have mounted them to hoist jugs, bags and other items from the dinghy as well as the outboard. The alternative is to use the mainsail boom and the topping lift but that involves using the mainsheet tackle as well.
 

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You could make a 12-18" sleeve bracket to withstand the moment at the bracing arm of the hoist. The real question is what is used to hold the mast in place.
 

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The schematic doesn't denote wall thickness or alloy of the tube in question. The tube would need to be at least .090 of 5052 alloy . Naturally .125 wall thickness would be better but probably unlikely for this application. I would question adding shear forces to anything thinner than .090 even with a sleeve or shoulder bracket.
 

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Garhauer uses stainless 2'" tube. The OP said his 3" tube was aluminum which requires additional wall thickness and or OD to obtain the same strength as stainless. If the OP's tube is .090 5052 then yes it is up to the task at hand. 063 would probably work but I wouldn't want to bet my engine on it.
 

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When I bought this boat, it had an outboard hoist with a 2” aluminum tube for a 4HP motor. When I got a bigger motor, I was worried about how strong it was. I solved the problem by putting a piece of 1/8” thick flat aluminum bar stock inside the tubing, aligned with the hoist arm. That was 20 years ago. It lifts a 25HP Yamaha outboard just fine.
 

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Discussion Starter #13
45 feet? Davits.
The previous owner's son removed them to avoid paying for a 50' slip ( an additional $2376 per year) since the slips in So. Cal are priced LOA including bowsprits and davits. Even on my prior boat with davits we would dismount the dink and put it on the foredeck and mount the outboard inside the pushpit for any offshore passage. Also the dink would fill with rainwater ( even with the drain open) when unattended while on the davits.
 
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