# Bunks on Alum boats with hull strakes -Where to place bunks?



## Tin Man

Hello all--

I'm back in the tinny world! I was going to purchase a 20'-22" Pontoon boat and decided that a small alum boat was more practical, economical, and a fun project. I believe the smaller the boat the more prone we are to use it!

I have a great lake in my city that has great LMB and Striper fishing. Excited about using my new boat out there and slaying some fish! Also excited about the many projects I can apply to my boat....many of which I have seen here on this board!!

Picked up a 2009 Bayrunner 15 last week! Excited about the simplistic approach to fishing/boating and the projects that can be accomplished on a small alum boat. 

Trailer set up question....

My Bayrunner has strakes on bottom of hull that are spaced at 2.5" apart. This space does not allow for a carpeted 2"x4" to fit between them. On a previous alum boat, the owners manual stated not to place bunks boards under strakes; ensure they were between them. On that particular boat the strakes had more distance between them, allowing for 2x4 placement between them. I'm assuming the same applies here.

So, what options do I have? 

Rip 2x4 down to a 2X2?
Use 2x4 on its ends (would require a different mounting bracket)?

Thoughts?


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## Scott F

Turn the 2x4 on it's edge so the narrow edge is between the strakes.


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## richg99

Yep, plenty of tinnys have the 2x4's on end. 
Yes, you probably will have to buy different brackets, or modify the ones that you have. 

I never did it, but imagine you could simply cut 2 extra pieces of 2x2s; screw them onto the lowest side of the upright present 2x4, and use the brackets that you already have. 

(I haven't given this idea all that much thought, but it would be worth thinking further about and playing with on your own boat.)

https://www.etrailer.com/Boat-Trailer-Parts/CE-Smith/CE10603G.html


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## Tin Man

I'm a little concerned about the smaller footprint the 2x4 on its side gives. 
I much prefer a wider footprint to spread the load...especially on the pothole-riddled roads in my town!!!

Do any of you run your bunks in a different manner or used a different solution?


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## richg99

The most you are going to get is the 2.5 inches that your strakes allow. 

Turn your 2x4 on its side...then add a 1x4 on the side. The 2 inch is really 1.5 inches. The 1 inch is really 3/4 of an inch. Your result will be 2.25 inches of wood. 

If you top it with thin carpet, you will just make your 2.5 inches. If the carpet is thicker, then you will have to rip ( or have someone rip) the 1x4 to a thinner dimension. 

Alternatively, you could use a router and trim a small diagonal portion off of the top of your new bunks, tapering them to accommodate the carpet. It all depends on your woodworking tools and skills.

One used boat that I bought came with upright 2x4 bunks. I was able to turn them flat. But, it was fiberglass and had a very flat bottom.

regards,


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## Tin Man

I like the idea of adding the 1x4 to the side of the 2x4. It may just work.

How would you attach the 1x4 to the 2x4? 

What about ripping a 2x4 down to the 2.5" needed? This would allow the wood to flex to contour of the hull easier than a 2x4 on its side. It may also allow me to use the current bunk brackets I have now.

Need to verify if the bunk bracket will fit the 2.5" wood. Mounting holes (which attach with #14 hex head wood self-taping screws) of the bracket are about 2" on center which may be too close to end of wood...splitting wood on insertion.


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## LDUBS

Tin Man said:


> I like the idea of adding the 1x4 to the side of the 2x4. It may just work.
> 
> How would you attach the 1x4 to the 2x4?
> 
> What about ripping a 2x4 down to the 2.5" needed? This would allow the wood to flex to contour of the hull easier than a 2x4 on its side. It may also allow me to use the current bunk brackets I have now.
> 
> Need to verify if the bunk bracket will fit the 2.5" wood. Mounting holes (which attach with #14 hex head wood self-taping screws) of the bracket are about 2" on center which may be too close to end of wood...splitting wood on insertion.



If you have bunk/bolster brackets that work like the one shown below, then adding a 1x4 to the side will result in your edge-wise bunks being off center to the bracket. No matter how much you tighten them, they would be constantly wanting to twist, which would be a real PITA and not good for your boat. In fact, even if perfectly centered using edge-wise bunks with this kind of bracket is probably not a good idea. You can replace the swivel part of the brackets with ones made for vertical bunks, but that would probably cost more than just replacing the whole bracket with the correct style (like in Rich's link).





Hey - I just made post number 1,000! WooHoo!!


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## richg99

There is nothing wrong with ripping the 2x4 to whatever width you want, and whatever width will fit both the brackets and/or the strake opening. If you want more flex, then that is the way to go. 

I am not sure that I understand ...."Need to verify if the bunk bracket will fit the 2.5" wood. Mounting holes (which attach with #14 hex head wood self-taping screws) of the bracket are about 2" on center which may be too close to end of wood...splitting wood on insertion.".... but anything can be modified or re-drilled to do what is necessary. 

Necessity is STILL the mother of invention.

The only thing that I can add is ...give yourself some room to fit the strakes between your bunks. It is a constant problem and discussion here and on other sites about getting the bunks katty-whampus /diagonally/or off-center relative to the strakes. 

Then, finding the amount of force that it takes.... to actually lift the whole boat and re-center.... is not a joyous event. 

Another method of re-centering is to back the boat in and start all over. 

I am old. I have added a power winch. After doing some rigging, I can clip the hook onto my boat and let the winch pull it up from the center all the while straightening the hull relative to the strakes and the bunks.

There are many ways to skin the cat.


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## LDUBS

Hmmm, had another thought building on Rich's comments. You could leave the existing 2"x4" bunk and put a 2"x2" or 2"x2.5" right on top of it. I've never seen it done this way but maybe it would work. Kind of like this:


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## richg99

LDubs...I like it. 

The only issue I can see is that you would be moving the boat HIGHER relative to its wheels. That can cause an issue on shallow ramps. 

Yet, that could be combatted by lowering the supports. Most of them have lots of adjustment space available. Or, flip the axle over if the trailer allows it.


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## Tin Man

I'm leaning towards the 2x2.5 on top of 2x4. Lowering bunks is not an issue as there is plenty of adjustment. 

NOTE: Called an alum boat builder here in CA (similar to my boat) and he stated that due to the spacing between strakes (2.5") it really didn't matter if bunk boards were directly under strakes. The proximity of strakes added hull strength to bottom...also considering weight of hull is about 300#, if that.


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## richg99

*"The proximity of strakes added hull strength to bottom.."*

I've always felt that strakes have two roles. One is to strengthen the thin aluminum sheeting, and the other is that the strakes provide some prevention from the hull sliding out in turns. 

Years ago, I had a number of flat bottom fiberglass boats ( 3 were Carolina Skiffs). Sliding out in turns was a daily occurrence, unless you slowed way down or turned more gently.


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## Tin Man

So......does it really matter if bunks boards are directly under/partially under strakes?
Is the concern that any bouncing of boat could damage strakes?
Are there other concerns?


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## thedude

Would think if you had bunks contacting two strakes would be fine. Contacting one would not be good.


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## richg99

Every one that I have ever seen or used personally have been between the strakes.

Due to gravity, I think the boat will want to position itself between the strakes, no matter what you do.


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## overboard

I have two 2x4's setting upright on one of my trailers, but it also has a wider center board that goes down the middle, so there are 3 load bearing surfaces on the hull, that was set up for a 1654 FB GRIZZLY and never had a problem. 
On a V hull I would put V type rollers down the center for the keel to rest on, and then either 2x4's on end or do as Ldubs suggested, I also try to keep the bunks between the chines for centering the boat on the trailer and so that it doesn't shift too much side to side while trailering.


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## LDUBS

Soooo, whatever you decide, fine tune your bunks so the boat sits just right. Add some tall side guides and adjust them so the boat has minimal side-to-side movement. If everything is adjusted just so, when you pull the boat out it will settle right down on those bunks just where it is supposed to sit. 

Have fun.


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## Tin Man

I'm leaning on ripping a 2x4 to a 2.5" width.

Concerns about other option: On ends, and adding a ripped 2x4 on top of a 2x4, reduces the flexibility of such bunk. Although there is not much curvature to my hull, there is some and I would want the bunk to flex as needed.

I'm just wondering if a ripped 2x4 (2.5"X3/12") is enough strength for the weight of hull (300#), outboard (160#), battery, fuel, gear, etc (440#) APPROX TOTAL 900# ?

???


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## LDUBS

Tin Man said:


> I'm leaning on ripping a 2x4 to a 2.5" width.
> 
> Concerns about other option: On ends, and adding a ripped 2x4 on top of a 2x4, reduces the flexibility of such bunk. Although there is not much curvature to my hull, there is some and I would want the bunk to flex as needed.
> 
> I'm just wondering if a ripped 2x4 (2.5"X3/12") is enough strength for the weight of hull (300#), outboard (160#), battery, fuel, gear, etc (440#) APPROX TOTAL 900# ?
> 
> ???




You are saying you want to rip a 2x4 (1.5x3.5) down to 1.5x2.5. Personally, I would not do that. Instead, I would elect to use the 2x4 on edge as previously discussed. This is a very common approach. In fact I may see as many "on edge" bunks for small boats as I do flat bunks. I don't think I have ever seen a 1.5" x 2.5" bunk (and yes, I do think I would notice). In my mind, there must be a pretty good reason why "on edge" 2x4 bunks are so commonly used -- they work. 

The downsides have already been mentioned. First, you probably should invest in new bunk brackets for the "on edge" config. These are pretty affordable. Second, your boat will sit 2" higher which could make it harder to launch or recover. As already suggested, perhaps you can adjust your bunk brackets down to offset this. 

Another suggestion I would offer is when all is said and done, make sure your boat's transom is fully supported by the bunk right under the transom. 

(BTW, 440# for gaso, batteries, and other gear seems like a lot, IMO.)

Edit: I meant to also say you might have to bevel the top edge of the 2x4 bunk to match your hull dead rise angle.


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## WV1951

Does your trailer not have any center rollers for the middle rib/strake to rest on?


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## Tin Man

Update....

Rollers:
I added a 12" roller far forward (hull has scrapped tongue in past) and flipped the oem forward roller back towards stern. This will prevent hull from ever touching/scrapping any metal part of trailer. I have been told by builders (Gregor and Klamath) to NOT allow boat to rest on rollers....weight should be carried by bunks. Based on this info I set rollers down as low as possible and raised bunks a little to achieve virtually no weight on rollers; they just kiss the boat. I can actually turn the rollers by hand which tells me that are adjusted properly.

Now, Bunks Boards update....

With all of the input and advice, it got me thinking.....

Since I want the bunks to flex to curve of hull and also flex while traveling down bumpy roads.....

A. Upright 2x4s would not allow as much flex as laying down 2x4s (standard mounting method)
B. Adding a 2x2 on top of 2x4 reduces flex tremendously
C. How about notching the 2x4 .....down to 2.5" wide (width between strakes) and 1/2" down (depth of strakes). This will allow use of 2x4 flat, allow for flex, and still fit snugly between strakes. Would there be enough wood after this notching to allow for solidly/firmly attaching the 2 lag screws?

Thoughts on C?

Thanks

Roller Pics:


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## richg99

Hmmmm. You are placing a lot of emphasis on allowing the bunks to bend to the curve of the hull.

I may be wrong, but I see Support as Support.

Walking near a line of trailers at any launch site, I don't recall seeing any that curve to fit????


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## LDUBS

My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem. 

PS: Agree you are probably overthinking the bunk flex thing.


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## WV1951

I am having trouble getting a grasp on this whole thing. My Mirro has a very heavy duty rib running the entire length the of middle. With the fact it is a rib, makes it doubly rigid and of course is riveted to the hull. There are two additional ribs/strakes in the same line next to the middle one. I would think this would make for a very rigid hull and supporting the weight would not be a problem. My trailer has two middle rollers, plus the bow stop. The bunks carry most of the weight, so the rollers would not be carrying that much.
When I had my boat upside down when painting, I saw no indication of the middle rib having any bend what so ever. The boat is 40 years old.
Maybe I am missing something.


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## Tin Man

LDUBS said:


> My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem.
> 
> PS: Agree you are probably overthinking the bunk flex thing.




Do you think where my rollers have been set up, they are correctly positioned? 

I kept the forward-most roller off of the forward bow portion alum piece and placed it under the center hull strake (is this center strake which is wider that the smaller strakes to port and starboard, called a keel strake)? 

I've been know to overthink too much!!

As far as the bunk boards......how does my latest idea sound?


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## Tin Man

richg99 said:


> Hmmmm. You are placing a lot of emphasis on allowing the bunks to bend to the curve of the hull.
> 
> I may be wrong, but I see Support as Support.
> 
> Walking near a line of trailers at any launch site, I don't recall seeing any that curve to fit????



I am thinking that once weight is placed on 2x4s, they flex. Mostly return to shape after weight is removed?


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## Tin Man

WV1951 said:


> I am having trouble getting a grasp on this whole thing. My Mirro has a very heavy duty rib running the entire length the of middle. With the fact it is a rib, makes it doubly rigid and of course is riveted to the hull. There are two additional ribs/strakes in the same line next to the middle one. I would think this would make for a very rigid hull and supporting the weight would not be a problem. My trailer has two middle rollers, plus the bow stop. The bunks carry most of the weight, so the rollers would not be carrying that much.
> When I had my boat upside down when painting, I saw no indication of the middle rib having any bend what so ever. The boat is 40 years old.
> Maybe I am missing something.



I believe that is what I am trying to achieve by adding the 12" roller and reversing the forward-most roller to sit under keel strake. 

It's the bunk boards that is my latest over-thinking dilemma!!! :shock: #-o


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## LDUBS

Tin Man said:


> LDUBS said:
> 
> 
> 
> My old boat was a 15' Klamath. The manufacturer was very clear that the boat should be supported on the trailer by the bunks at the transom and the roller up front under the bow stem.
> 
> PS: Agree you are probably overthinking the bunk flex thing.
> 
> 
> 
> 
> 
> Do you think where my rollers have been set up, they are correctly positioned?
> 
> I kept the forward-most roller off of the forward bow portion alum piece and placed it under the center hull strake (is this center strake which is wider that the smaller strakes to port and starboard, called a keel strake)?
> 
> I've been know to overthink too much!!
> 
> As far as the bunk boards......how does my latest idea sound?
Click to expand...


Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). Take a look at page 126 of the "Pic of Your Boat" category. Captain Morgan has a side view pic of his boat on the trailer. While his boat is shorter than yours, in my mind that same concept should work for you. Hope this helps.

As far as the bunk configuration, if it were me I still think having them on edge is easiest and will work well to support your boat.

Also take a look at WV1951's thread just adjacent to this one. He has a great pic of his trailer without the boat. That same set up should work well for you. WV1951 and I might debate the need for the rear-most roller but the concept is still the same. (sorry about all the edits).


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## Tin Man

*LDUBS wrote:*
[/quote]Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). [/quote]

What would be the reason for the rear roller not touching hull when loaded but the front roller can touch? Currently, both rollers can be turned by hand while boat is loaded.....this indicates full hull weight is supported by bunks.

To achieve what you suggest, I would have to raise forward roller higher than rear roller, as rear roller is bottomed out on its bracket. Front roller is not as easy to raise in multiple increments.

I also was wondering under which portion of the bow should the forward roller be resting......forward-most bow aluminum (from tip of bow down to where it connects with keel strake) or slightly larger center keel strake? 
And why?


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## LDUBS

Tin Man said:


> *LDUBS wrote:*


Hi TinMan. I think I experienced a similar issue and understand why you put the 12" roller where you did. However, IMO it should not be touching the boat when the boat is fully loaded on the trailer. The only roller that should be touching the boat when fully loaded is the one under the bow (the one you flipped back). [/quote]

What would be the reason for the rear roller not touching hull when loaded but the front roller can touch? Currently, both rollers can be turned by hand while boat is loaded.....this indicates full hull weight is supported by bunks.

To achieve what you suggest, I would have to raise forward roller higher than rear roller, as rear roller is bottomed out on its bracket. Front roller is not as easy to raise in multiple increments.

I also was wondering under which portion of the bow should the forward roller be resting......forward-most bow aluminum (from tip of bow down to where it connects with keel strake) or slightly larger center keel strake? 
And why?[/quote]

My reasoning for not having the rear-most roller against the boat in your application is to avoid putting a divot in the bottom of your boat. Keep in mind it is not needed to support the boat. You would be adding a third contact point between the front and rear supports. If it is not perfectly adjusted and if the boat & trailer don't move as a single unit, that roller can act as a pivot point when your boat bounces. I don't think I'm describing this very well, but hopefully you get what I mean. Note that others do not share this concern and I am sure you will find plenty of examples of multiple rollers along the keel. Ultimately it is your call. 

I hate like heck to open another potential can of worms here, but you say the rollers are close but not touching. I'm not sure how 100% of your boat is supported by just the bunks. If (when) your boat bounces just make sure it won't be pounding against one of both of those two rollers. 

I'm not an expert. This is all just my opinion based on my experience with a similar boat and the guidelines given by Klamath.


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