Antenna for a small boat

[Digger84]

Would a 1/2 wave antenna be the best bet to mount on a small fishing boat since it wouldn't need a ground plain? It's an aluminum boat but I would be mounting it on the back corner of the boat so it wouldn't have an even metal surface under it.

[kidphc]

most marine atennas take into consideration the lack of ground plane. Either by 1/2 design or by using part/all of the coax as the ground plane.

Here is a good place to start narrowing down you choices. Although these are VHF design.

I do not endorse either site. Simply to start pointing you in a direction.

West Marine UHF marine antennas.

defender Marine antennas

Edited December 2, 2022 by kidphc
Technical correction

[gortex2]

That link goes to VHF not UHF

But as said a 1/2 wave will work ok. To be honest a 1/4 wave on an L-bracket bolted to boat will most likely suffice unless your traying to talk 50  miles. We ran one on our fire boat for years and it was fine.

[kidphc]

5 minutes ago, gortex2 said:

That link goes to VHF not UHF

But as said a 1/2 wave will work ok. To be honest a 1/4 wave on an L-bracket bolted to boat will most likely suffice unless your traying to talk 50  miles. We ran one on our fire boat for years and it was fine.

Sorry yeah came back to correct the post. They are VHF antennas

Are you suggesting something like this or just a simple l bracket without ground planes? 

Mobile to base gound plane bracket

I plan on using one personally for the eaves to a house. A thin mobile design would hide better from the HOA then a 17' white fiberglass on a 40' mast.

[BoxCar]

You can also use a J-Pole as it has an integral ground plane.

[KAF6045]

2 hours ago, gortex2 said:

That link goes to VHF not UHF

Probably not too surprising... The maritime radio band is upper VHF, and they likely stock antennas for that usage.

 

[Digger84]

Thanks everyone for the advice. I might try that 1/4 wave idea first since I am planning to replace the one on my truck that came with my MXT275. I don't get to far out with boat so the 1/4 wave that came with it just might work for what I need. Thanks again everyone.

[gortex2]

More like this with a 1/4 wave UHF NMO on it. The midland antenna is not that great. 

 

 

[Digger84]

6 hours ago, gortex2 said:

More like this with a 1/4 wave UHF NMO on it. The midland antenna is not that great. 

 

 

Ok that looks perfect, now I think I understand what you meant. Yeah I haven't been real impressed with what came with my Midland.

[KAF6045]

1 hour ago, Digger84 said:

Ok that looks perfect, now I think I understand what you meant. Yeah I haven't been real impressed with what came with my Midland.

I'd prefer a larger ground plane for 1/4 wave. A 6.5" square or disk is about right (for the low end of GMRS, repeater inputs would be a tad smaller).

[wayoverthere]

8 hours ago, KAF6045 said:

I'd prefer a larger ground plane for 1/4 wave. A 6.5" square or disk is about right (for the low end of GMRS, repeater inputs would be a tad smaller).

Such as this? https://theantennafarm.com/shop-by-categories/shop-all/antenna-accessories/misc-antenna-parts/11713-taf-disc346-detail

[SteveShannon]

1 hour ago, wayoverthere said:

Such as this? https://theantennafarm.com/shop-by-categories/shop-all/antenna-accessories/misc-antenna-parts/11713-taf-disc346-detail

That one is only 19 ga. thickness. It’s meant to be attached to a fiberglass roof. 
A cookie sheet, pizza pan, or pie plate like this will work:

10 Inch Round Pie Pan for Baking, Aluminum Commercial Grade Pie Plate by Tezzorio https://a.co/d/2fHKb9h
 

Don’t let us convince you that the size is too critical. These antennas are typically fastened to a metal roof of indeterminate size. Also you’re on the water. That’s just perfect in terms of terrain. 
I’ve never put an antenna on a boat, and I don’t know what your boat is like or what it has for mounting, but do whatever is easiest. 

Edit: I told I’d never put an antenna on a boat. It appears that for marine applications the body of water serves as the ground plane. I really don’t know how you take advantage of that. 

Edited December 3, 2022 by Sshannon
Learning as I go. Sometimes slowly.

[WRUU653]

3 hours ago, Sshannon said:

It appears that for marine applications the body of water serves as the ground plane. I really don’t know how you take advantage of that.

I have never done this either. It seems to me that the aluminum boat in the water would be ideal for a grounding plane. My thoughts are you could almost attach it anywhere.  That said many here know more about antennas than I and I haven’t found much on the subject as it relates to aluminum boats.

 I have been following this thread because we had an aluminum boat we took out in a bay regularly when I was growing up. This would have been a great way to communicate back when my brother and I were going out on the water.   Many times people (tourists unfamiliar with the concept of tides) would go out on the bay, then get stuck when the tide went out. Not much to do but wait for the water to come back. A radio would be great to get that info to them provided they had one.  

[KAF6045]

While focused on marine band, http://www.boat-project.com/tutorials/vhfant.htm, may offer some insights. For ground-plane, it implies one needs a solid grounding route from antenna and/or radio through to the aluminum hull.

[Digger84]

So if I understand this correctly if that NMO L bracket is attached directly to the aluminum body of the boat then the water and boat will work together as a ground plane? One thing I hadn't thought about was having the antenna at least 3 ft from anyone in the boat, is that a pretty standard rule of thumb?

[SteveShannon]

18 minutes ago, Digger84 said:

So if I understand this correctly if that NMO L bracket is attached directly to the aluminum body of the boat then the water and boat will work together as a ground plane? One thing I hadn't thought about was having the antenna at least 3 ft from anyone in the boat, is that a pretty standard rule of thumb?

I don’t know what power you’re outputting, but you’re probably not going to be transmitting at a high duty cycle. I assume you’re not going out on the boat to talk on the radio. If you put the radio onto a mast you’re in even better shape.

I would be sure and get some oxide preventing compound to put between all the metal pieces.  Any electrical supply store or even Ace or Menards should have it. Aluminum oxidizes very quickly and aluminum oxide is very hard and non-conductive.  Then, when you’re ready to attach the bracket, sand the contacting surfaces and apply the oxide preventative before attaching them together.

[Digger84]

Yeah it would mostly be so my wife can get a hold of me since there isn't great cell service in the area and I've been known to drop my phone before!!! I was just looking it over and I could mount it at top of the pole the white light is on. That would put it about 2 ft above me. Thanks for the tip about the oxide prevention I hadn't thought of that issue.

[SteveShannon]

1 minute ago, Digger84 said:

Yeah it would mostly be so my wife can get a hold of me since there isn't great cell service in the area and I've been known to drop my phone before!!! I was just looking it over and I could mount it at top of the pole the white light is on. That would put it about 2 ft above me. Thanks for the tip about the oxide prevention I hadn't thought of that issue.

That sounds perfect!

[WRUU653]

Used this stuff a bunch for electrical, a thin film is really all you need. 

[Digger84]

Looks like our local Home Depot has that Noalox, thanks for the tips on that. Since I am now looking at mounting the antenna on the pole that the white light is on I will need to run a wire down to the boat body from the L bracket right to create the ground plane since the pole it's on doesn't seem to be a very good electrical conducter as far as I can tell so far. So I would use that noalox at the point the wire connects to the boat and would I still get the same ground plane effect from the antenna being roughly almost 3 ft above the boat?

[SteveShannon]

14 minutes ago, Digger84 said:

Looks like our local Home Depot has that Noalox, thanks for the tips on that. Since I am now looking at mounting the antenna on the pole that the white light is on I will need to run a wire down to the boat body from the L bracket right to create the ground plane since the pole it's on doesn't seem to be a very good electrical conducter as far as I can tell so far. So I would use that noalox at the point the wire connects to the boat and would I still get the same ground plane effect from the antenna being roughly almost 3 ft above the boat?

Yes. But you might also be able to improve the connections with and apply the noalox. Short jumpers are used to bond parts together to improve the ground system. There are several videos on marine bonding on YouTube. I haven’t watched any of them. 

[Digger84]

Ok so I could possibly improve the connection through the existing pole with some short jumpers especially it looks like where it meets the boat body. That makes sense I hadn't thought of that. Thanks . I'll check out those videos also