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Author Topic:   Antenna extension mast
wally910 posted 05-22-2014 09:31 PM ET (US)   Profile for wally910   Send Email to wally910  
I've been tinkering with the idea of adding an extension for my gam electronics whip antenna. I'm thinking 4 ft or so. I am wondering about using PVC for the extension. Has anyone ever tried this? I tried searching but couldn't find anything.
contender posted 05-22-2014 11:44 PM ET (US)     Profile for contender  Send Email to contender     
Should work, running the cable inside the pvc, need a good way to attach it to the hull/boat
jimh posted 05-23-2014 12:11 AM ET (US)     Profile for jimh  Send Email to jimh     
Wally asks:

Has anyone ever tried [using an extension mast in conjunction with a GAM SS-2 antenna]?


wally910 posted 05-23-2014 06:24 AM ET (US)     Profile for wally910  Send Email to wally910     

I've read that post. In fact, it was the reason I went with the GAM antenna. However, didn't see anything about PVC in it. I'm trying to avoid spending the 50-75 dollars on the Shakespeare mast.

Jefecinco posted 05-23-2014 09:58 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
The Shakespeare mast is strong fiberglass. PVC pipe is relatively weak. Furthermore the pipe would have to be adapted to fit the Gam and an antenna mount with a lay down feature.

I have the cited set up on my Montauk and the loading on the antenna extension mast and ratchet mount is high whenever the boat is on plane or moving around. Based on my experience I would not attempt to use PVC pipe for an antenna mast.


jimh posted 05-23-2014 10:27 AM ET (US)     Profile for jimh  Send Email to jimh     
wally replies:

I've read that post. In fact, it was the reason I went with the GAM antenna. However, didn't see anything about PVC in it. I'm trying to avoid spending the 50-75 dollars on the Shakespeare mast.

I am pleased to hear that my article recommending the GAM SS-2 antenna influenced your decision on what antenna to buy.

It was not clear to me if your inquiry was specifically asking for advice about using PVC as an extension mast or if you were just asking about use of extension masts, because you referred to the object of your question with the pronoun "this." I didn't know if "this" referred only to PVC or to using an extension mast.

The Shakespeare extension mast I used is mentioned in the article. It is a Shakespeare 498 extension mast. It is described as white polycarbonate. It is not very expensive--that is one of the most important qualities for my use and recommendation. I think at the time I bought one the price was $35. Perhaps they are a few dollars more, today. I would be very surprised to find their price has doubled to $75. You can order one from DEFENDER for $41. id=70753

If you want to make your own extension mast, I believe that a four-foot piece of PVC pipe or tube could be used as an extension mast, but it might have a bit more flexibility than the Shakespeare 498 extension mast. The flexibility is probably not the most important concern. I am not familiar with the strength of the typical PVC adhesives. I would be concerned about the attachment of the PVC threaded fittings to the PVC pipe.

A few years ago I bought some PVC fittings and pipe for the purpose of experimenting with them as part of a new antenna design. I am afraid I have not gotten any further on that project. I cannot offer any first-hand experience with PVC as part of an antenna or mast. But my speculation is that it would be quite useful, particularly if you did not plan to operate the boat at extremely high speeds, when wind loading on the mast would be much higher than usual.

jimh posted 05-23-2014 10:49 AM ET (US)     Profile for jimh  Send Email to jimh     
The material used in the Shakespeare 498 extension mast is not a fiberglass laminated tube. The longer, fancier, and more expensive extension masts made by Shakespeare are made with laminated fiberglass, but the Model 498 is just a straight tube and appears to be molded or extruded, not laminated.

You can buy polycarbonate tube, but it may be more expensive than just buying the Shakespeare mast. GRAINGER sells an eight-foot length of 1-inch OD tube for $32.55. See

This material has a tensile strength of 9,200-PSI.

I don't know what sort of adhesives work with polycarbonate. They might be expensive. I don't know of a convenient source of threaded pipe fittings for polycarbonate.

HOME DEPOT sells 3/4-inch CPVC pipe, which has an OD or 0.875-inch. That material is said to have a "rating" of 400-PSI, but I think that might be a specification for its burst strength for containing a fluid under pressure.

http:/ / www. homedepot. com/ p/ Charlotte-Pipe-3-4-in-x-10-ft-CPVC-SDR1 1-Flowguard-Gold-Pipe-CTS-12007-0600/ 100161617?N=5yc1vZbuy7#specificati ons

The tensile strength of CPVC is described as 8,200-PSI at

This is quite comparable with the polycarbonate material used in the Shakespeare 498. Based on that figure, I don't see why you couldn't make your own extension mast with CPVC pipe and fittings. A four-foot length of pipe ought to cost no more than $5 and the fittings are about $1 to $2.

wally910 posted 05-23-2014 02:38 PM ET (US)     Profile for wally910  Send Email to wally910     

Thanks for the clarification. I was not aware of the less expensive option offered by Shakespeare. The only extension I was aware of was the more expensive fiberglass option.

I think I will experiment with the PVC extension. I will probably opt for schedule 80 PVC, which has thicker walls and is rated for higher pressure than is the typical schedule 40.

jimh posted 05-25-2014 07:53 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is a chart of CPVC pipe dimensions: schedule-40-dimensions

The above (linked) chart say the OD of Schedule 40 3/4-inch pipe is 1.050-inch, with a wall thickness of 0.113. This sounds like a decent material to make an extension mast, if the mast is only going to be four-feet long.

Jefecinco posted 05-25-2014 10:30 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
If pipe is used it will look more integrated, if that matters, if a little Krylon or similar paint is used to dress it up.


jimh posted 05-25-2014 02:16 PM ET (US)     Profile for jimh  Send Email to jimh     
Butch--I agree with your recommendation to use some paint on the CPVC or PVC pipe and fittings, and I like KRYLON paint, too. Unfortunately, since KRYLON paint is about $6 per can, you are going to double the cost of the mast.

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