Best way to mount this?

[Grizz]

Hi all - First time tin boat owner and first time DIYer with anything really, so looking for some newb-friendly guidance.

What do you think the best way to mount this bracket to the gunnel is? The goal is to ultimately mount a 55 lb thrust Haswing Cayman bow mounted trolling motor on it (think the motor itself weighs about 60-65 lbs).

Ideally I bolt it, but the lip of the gunnel that I would be able to drill through is pretty narrow. I'm not able to drill straight down the center of the rounded gunnel, it would need to be on the right third of the gunnel, and then I'm still not sure if nut would fit on the bottom or how secure it would be since the bolt and nut would be making contact with the gunnel at an angle. Don't think I can use rivets as it's a rounded surface.

Wonder if I can just use 4200 (or maybe 5200?) and use no hardware?

Planning on using well nuts or rivets to secure the other side of the bracket to flat deck.

 

[DaleH]

Riv-nuts, well-nuts and 5200 for sure won't hold the weight nor survive the torque ...

Can you provide an overhead picture 'looking down' so we can see the deck and all?

That said, for that use, IMHO you need to through-bolt it. Somewhere in the vicinity I'd drill the deck for a 4" water-proof inspection deck plate/port; cheap, available in various colors, and provided underneath access to the deck.

Before mounting that plate/port, drill your trolling motor plate in place and reach your hand/arm, or that of a skinny helper, in through the deck plate hole to affix wide nylon washers, and add large diameter SS fender washers to securely bolt it to the deck. You might even just be able to add the mount itself without that tin piece ... not sure.

Then rivet the flange for the inspection deck plate/port in place, lube O-Ring and groove with dielectric grease and install. Done ...

....

 

[Grizz]

Riv-nuts, well-nuts and 5200 for sure won't hold the weight nor survive the torque ...

Can you provide an overhead picture 'looking down' so we can see the deck and all?

That said, for that use, IMHO you need to through-bolt it. Somewhere in the vicinity I'd drill the deck for a 4" water-proof inspection deck plate/port; cheap, available in various colors, and provided underneath access to the deck.

Before mounting that plate/port, drill your trolling motor plate in place and reach your hand/arm, or that of a skinny helper, in through the deck plate hole to affix wide nylon washers, and add large diameter SS fender washers to securely bolt it to the deck. You might even just be able to add the mount itself without that tin piece ... not sure.

Then rivet the flange for the inspection deck plate/port in place, lube O-Ring and groove with dielectric grease and install. Done ...

....
Plate.jpg

Appreciate the quick reply.

Here are some more pics of the boat. It's a new 2022 Lowe 1448M. Not sure if this makes a difference or not, but the trolling motor will be mounted with a quick release bracket and the plan is to only have the TM on during times of use. So there won't be the "wear and tear" of it being mounted 24/7.

 

[DaleH]

What's that rectangular piece? Is that what needs to be mounted to the top of the front deck? Then a quick-release mount for the TM affixes on top of that?

Sorry, I only use tiller stern-drive TMs .

If so, maybe put a hatch cover on the vertical face of the bow deck, big enough to get your hands under there to through-bolt mount that rectangular piece. Likely it would then be handy for odd storage; spare lines, etc.

Or, if you drill drill down through the outer 3rd of the rond gunnel, instead of a flat jasher, you could fab a curved or 'J' shaped piece to bear up against the round gunnel, upon which a SS nut could seat.

 

[overboard]

I think I would do something similar to what Dalett suggested. Once you can gain access to the underneath of the deck there are ways to get in there with tools if needed, A nut can be held in place in a wrench using duck tape, a washer can be held on top of the nut using grease or glue, a wrench can be extended simply by taping a length of rod to it to make it as long as needed,
One thing that could be a PITB is if there is flotation foam in the bow, then you would probably need to remove some of it in order to access the bolts and install the nuts, washers' etc.
Another option is to weld it on.

 

[poorthang]

https://previews.dropbox.com/p/thumb/ABjo0qKraeyuAkhLqGc4gOKrBQNR40Yoya5Jb3ZZcaoFjw6WMxz7RWgYzJu2y469wP6DnHLFPiuEZvC6XGidHKvrT_mHlZX_mHbYlQRNSDCR03EHI0Bi7WB6Jnj39480sKtejnQtR84GIdZIsI0bNfGvNI6099hD7mUX7QECsDTijCSlVUxAtoHhLqH5PrnDubfao_K-re0Yq8UrjFEPlLaFX_BihXvvu_fuOXLTs0bms_4ZrtbdGE4Q13kbH465JJR-PbyB4VvGYcThkLV-YWUivlFR_BNpY8Sj8QJE20QqIODOBh8uP3XrT4OYZmnCro_lKXD26VtR93XJVGM6Kl0v4ZINLy34nrfOdUvtuaaOcpfG2jivKEZ4ctSgTJP0DbY/p.jpeg

my 1978 fisher from the factory. rough life, still very tight. the sides are winged and riveted under the carpet.
note, havnt got the hang of drop box, another photo in highlighted link.

 

[Grizz]

What's that rectangular piece? Is that what needs to be mounted to the top of the front deck? Then a quick-release mount for the TM affixes on top of that?

Sorry, I only use tiller stern-drive TMs .

If so, maybe put a hatch cover on the vertical face of the bow deck, big enough to get your hands under there to through-bolt mount that rectangular piece. Likely it would then be handy for odd storage; spare lines, etc.

Or, if you drill drill down through the outer 3rd of the rond gunnel, instead of a flat jasher, you could fab a curved or 'J' shaped piece to bear up against the round gunnel, upon which a SS nut could seat.

Mount.jpg

You are correct. That rectangular piece is the bracket I need to install onto the deck to be level with the gunnel. The quick release bracket itself will be bolted onto this rectangular piece, and then the motor installed on the quick release bracket.

I need a section of the deck to be level with the gunnel so that the motor can hang off the side of the boat so that it can be deployed into the water, hence the rectangular piece.

I am definitely going to bolt the quick release bracket (and therefore the TM itself will basically be bolted) onto that rectangular piece. I am hoping I can get away with well nuts or rivnuts, and maybe some 4200/5200, to get that rectangular piece mounted to the deck, and trying to figure out the best way to bolt the rectangular piece through the gunnel since the lip of the gunnel is narrow. I know you said the well nuts/rivnuts/5200 isn't enough to handle the torque, but wondering if that still holds true now that you have the additional info/pics? Again, the bracket itself that the motor will latch onto WILL be bolted through that rectangular piece.

 

[Grizz]

I think I would do something similar to what Dalett suggested. Once you can gain access to the underneath of the deck there are ways to get in there with tools if needed, A nut can be held in place in a wrench using duck tape, a washer can be held on top of the nut using grease or glue, a wrench can be extended simply by taping a length of rod to it to make it as long as needed,
One thing that could be a PITB is if there is flotation foam in the bow, then you would probably need to remove some of it in order to access the bolts and install the nuts, washers' etc.
Another option is to weld it on.

There does appear to be flotation foam within the bow. At least I can feel it from under, not sure how far up it extends in the bow.

 

[DaleH]

I'm afraid I'm going to have to defer to those who have mounted bow TMs before. I don't ever not through-bolt myself, with one rare exception, as I've seen every other fastener type loosen over time or to give away or fail. BUT admittedly my boating experience in 99% in saltwaters and the seas can be vicious!

So don't mind me, but I really don't want to steer you in the wrong way ...

In the event I can't through bolt (deck, safety, heavy or expen$ive items), I'll use either a SS 'Toggler' which is a fancy brand name of a marine toggle bolt (but I would not use one on a tin boat) or I would remove a mushroom shaped core of the frp boat and glass in a mushroom anchor with SS threads built in. Significantly elegant, yes
but yeah, lots of glass work.

 

[Macintosh]

No expert, but I have mounted several bow mount TM's and also seen a few destroyed gunwales from other folks trolling motors. A caveat, I also like my stuff to be rock-solid. You need that mounting bracket to be SOLID. Remember, it's not just 65lb of weight or 55lb thrust, its that with the leverage of a 45"+ shaft hitting a log or the bottom; even when stowed the motor is leveraging that mount every time you hit a wave or when trailering it, etc--and unlike a transom that deck area isnt likely braced or designed to support that kind of load. No way I would do this without some sort of through bolt, and to be honest I would be looking to reinforce the bottom-side of the deck with a large flat piece of something approximately the same size as the bracket itself (3/16" sheet aluminum, marine plywood, or something really beefy) to act as a giant washer to spread that torque out across that entire surface area rather than concentrated on 4 little holes in thin aluminum decking. At an absolute minimum, if you go with rivets or similar, I would want good-sized washers underneath that deck or I'd bet good money you'll pretty quickly deform and then pull them through the aluminum decking. I would also strongly consider some sort of brace under the head of the trolling motor to brace it against the deck or to the gunwale during transport to reduce the leverage on the bracket from bouncing in waves and when trailering.

Edit: check out the bracket on this boat: https://www.seaarkboats.com/boat/94/1648-mv-special That's a heavier boat than yours, but I bet if you gave them a call and just asked about how their trolling motor bracket is reinforced they'd tell you if they reinforce or if they just attach to the decking and how thick their decking is, etc.

 

[poorthang]

No expert, but I have mounted several bow mount TM's and also seen a few destroyed gunwales from other folks trolling motors. A caveat, I also like my stuff to be rock-solid. You need that mounting bracket to be SOLID. Remember, it's not just 65lb of weight or 55lb thrust, its that with the leverage of a 45"+ shaft hitting a log or the bottom; even when stowed the motor is leveraging that mount every time you hit a wave or when trailering it, etc--and unlike a transom that deck area isnt likely braced or designed to support that kind of load. No way I would do this without some sort of through bolt, and to be honest I would be looking to reinforce the bottom-side of the deck with a large flat piece of something approximately the same size as the bracket itself (3/16" sheet aluminum, marine plywood, or something really beefy) to act as a giant washer to spread that torque out across that entire surface area rather than concentrated on 4 little holes in thin aluminum decking. At an absolute minimum, if you go with rivets or similar, I would want good-sized washers underneath that deck or I'd bet good money you'll pretty quickly deform and then pull them through the aluminum decking. I would also strongly consider some sort of brace under the head of the trolling motor to brace it against the deck or to the gunwale during transport to reduce the leverage on the bracket from bouncing in waves and when trailering.

Edit: check out the bracket on this boat: https://www.seaarkboats.com/boat/94/1648-mv-special That's a heavier boat than yours, but I bet if you gave them a call and just asked about how their trolling motor bracket is reinforced they'd tell you if they reinforce or if they just attach to the decking and how thick their decking is, etc.

if you blow up their pictures, you will see 4 rivets on the rear bracket, 2 rivets on front. the one i pictured has rivets all the way down on both sides pus the ones on the front. you will bend the troll motor before you harm or loosen the bracket.

 

[gogittum]

The points already made are good ones. You'll need access thru the foredeck and there will be huge torque on that mounting bracket. (oh, mercy......here we go again with fighting pictures onto this forum )

[/img]

What I've done in the past with "pretty good" results is drill thru at a small angle to give a bit of room at the bottom, then take a nut the next size larger and drill the threads out of it to make a spacer. Then grind one end off at an angle to give a solid bearing surface for the actual tension nut. Use a washer between them.

That long, narrow mounting shelf is going to be twisted enormously hard and there isn't enuf surface at the ends to support it properly. Only option I can see is the one with the hatch in the foredeck and fabricate braces to anchor the rear of the shelf down. I think I'd use a much wider piece to give more support.

As always, the pictures aren't in the order I added them.

 

[gogittum]

Thinking further on this, when I built the bow cap extension on mine, I found a piece of aluminum diamond plate at the local scrap yard. I told the story of shaping it on here quite a while back and I had fits bending it. It's granite hard.

[/img]

I don't know if this stuff is 6061 or 7075 but it's the strongest I've ever seen and would be a very good choice for your application. Where I mounted my components, I used an angle grinder with cutoff wheel to verrry carefully cut the diamonds flush. You could dangle the whole boat from this thing and it'd grin at ya.

 

[eeshaw]

I think the first thing is to find out how thick the base metal is you're dealing with. SeaArk is going to be about an 1/8 inch so I wouldn't use it for reference. You want to spread the load over as much area as possible. I don't think you have any good alternative other than to have it welded in place. Probably not what you wanted to hear but that's the route I'd go. If your base metal is thin, like 1/16 inch you could lay in some stiffening panels to help reinforce the area also.

 

[Grizz]

Thank you all for the advice and recommendations.

I think I’ve settled on bolting through the top of the bracket, all the way through the gunnel. Then I will Rivet the bracket to the flat deck. For additional support, I will use 4 additional bolts that I will put through the side of the gunnel that will go through the side of the bracket which is folded over slightly.

This seems to be within my wheelhouse of comfort as I am popping my DIY cherry with this little project.

I found a video online where someone installs this exact bracket with just 4 rivets to the gunnel and 4 rivets to the deck and it worked out fine, so I think exchanging the gunnel rivets to bolts and adding additional bolts through the side will be even more secure and should work ok.

I guess the next thing I need to figure out is size/length/material of the hardware. The bolts I can figure out. But for the rivets, should I be using 3/16 stainless steel rivets with stainless steel mandrels? I know those are the strongest but not sure if I should use aluminum for an aluminum boat? And for the length of the rivet, should I get the longest possible that I can reasonably fit? Like is there any downside to having “too long” of a rivet as long as it fits?

 

[DaleH]

I think I’ve settled on bolting through the top of the bracket, all the way through the gunnel. Then I will Rivet the bracket to the flat deck.

If you want 6 or 8 or so, I have some high-shear 1/4" aluminum rivets, but you'd likely need the large 'A'-framed rivet tool to seat them.

I don't like mixing SS and aluminum unless you can separate or isolate the 2 materials from each other ... e.g., duct tape, nylon washers, etc., ... but it is hard to do whilst using blind rivets.

 

[gogittum]

All aluminum rivets aren't very strong. The force is applied on points and concentrates on each rivet. I've come to like the aluminum rivets with stainless steel mandrels. I'd use the 3/16" and use backing plates (washers) with each one. Buy them off the same rack as the rivets. Under heavy and/or repeated strain, the rivets can pull right thru the aluminum. The washers add a "lot" of strength.

The biggest thing I found is pulling them. The steel mandrels take a lot of force to pull and the little stamped out pullers don't give enuf power to pull them. I bent the handles on one, trying it. HF sells a heavy duty, 2 handled 17" puller for under $20 that is a jewel, even if made in China. It even has a little bottle to catch the pulled stems. Well worth it - makes pulling those heavy rivets quick and easy.

Edit: Just saw Dale's post - the 1/4" would be even better, but no way you'd pull them without the heavy duty puller.

 

[Macintosh]

I can't view the photos poorthang posted but sounds like he riveted with success, but note it sounded like he used a lot of rivets (??)--twice as many rivets is twice as much surface area to pull through the aluminum deck if the deck material isn't really beefy. I'm approaching this from most of my use being on a very large lake with pretty rough water, ime stuff like this typically breaks much more from cumulative wear and tear caused by motoring in waves or trailering on dirt roads than it does from actually using the trolling motor, so perhaps my advice doesn't apply to your situation or I'm just overly cautious...regardless, I don't think the issue is bending the bracket or the rivets themselves not being strong enough, I think the issue is over time bending and fatiguing the aluminum deck and pulling rivets through the aluminum deck the bracket is attached to. A buddy made a bracket similar to this on a jon boat years ago, his failed repeatedly by pulling successively-larger rivets through the aluminum seat he attached it to, mostly caused by stress from trailering. After the seat was jacked he cut it open and used a piece of sheet aluminum underneath the size of the bracket and through-bolted it, and it was fine from then-on. If that deck is full of foam and preventing an access underneath then welding or using many larger rivets might be best option to get maximum surface area of connection onto the thin deck material. Attaching to the gunwale along its length also would add a lot of strength and rigidity. I'm sure I'm recommending over-building it to a degree, but within reason I've yet to be sorry about making anything a little stronger than it probably needs to be.
Rivet choice, others probably better to give help.