# Trying to rebuild a simple Johnsen Skiff



## yobata (Jul 14, 2015)

Hi and welcome! I love seeing these rebuild threads. 

Foam: I wouldn't leave it exposed but others will hopefully chime in and give you more/better advice. I think a few forum members have found ways to bring the foam up off the bottom of the hull (under gunnel perhaps) 

Motor: since you will be buying a motor (I'm assuming new), I would opt for the 20" shaft. I think you will find it easier to resell if you ever decide to do that. On the other hand, it will weigh a bit more and you will need a bigger transom which will also add some weight. I went with a 15" transom because I bought a USED 2 stroke 25hp Yamaha - it's a great motor for my Johnsen.

Looking forward to following your progress!


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## JPizzle (Nov 9, 2017)

The foam would be up off the bottom of the hull. I was thinking to maybe flip the boat upside down when pouring in the foam and have it stick to the bottom of the deck. I could fillet in a piece of pvc from side to side to give the foam an anchor to the hull. I don’t plan to have any compartments or gunnels so it would just be front and back.


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## Emerald Shiner (Dec 26, 2017)

Coast Guard approved 2-part buoyancy foam can not absorb water.


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## Backcountry 16 (Mar 15, 2016)

Your poling platform I would have custom made and my reason for this is if you use a tiller extension you will lose some steering ability as your extension will hit the platform. I opted to pick up a casting platform and it has worked really well so far.


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## DuckNut (Apr 3, 2009)

Emerald Shiner said:


> Coast Guard approved 2-part buoyancy foam can not absorb water.


I beg to differ with you and most people who have rebuilt a boat will too.

Pizzle. If you want to keep the foam off the floor you can accomplish this. I will explain how to do the bench and translate that to the bow.

Your foam does not need to be the two part and can be any type of foam. Cut the top off the bench and fit a false bottom inside and close the sides so the foam doesn't drip through and to the bottom. Then reattach the top and cut a couple holes in the top and fill it up.

This will keep the foam off the floor where it will absorb the water quickest.

People have also used pop bottles and pool noodles.


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## JPizzle (Nov 9, 2017)

I have looked at other foams such as the dow billets for floating docks. I am going to stick with the pour in type, but won’t be completely concealing it in a compartment. I will come up with a way to install but be able to remove easily if it becomes an issue. Being a contractor, I have drawn the plans for this and revised a bunch of times already.


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## Emerald Shiner (Dec 26, 2017)

DuckNut said:


> I beg to differ with you and most people who have rebuilt a boat will too.
> 
> Pizzle. If you want to keep the foam off the floor you can accomplish this. I will explain how to do the bench and translate that to the bow.
> 
> ...


If you are re-building a boat then it wasn’t done correctly the first time. If the foam is waterlogged then they used the wrong foam.


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## WhiteDog70810 (May 6, 2008)

Turning the boat over and pouring 2-part foam between the deck supports is a great idea. I wish I did it that way. If you want an excuse to learn to vacuum bag, you can be really fancy and cut the foam off level with the supports and then vacuum bag a layer of glass over the foam to protect it from the day-to-day wear and tear.

I epoxied pink extruded polystyrene under my decks. That is a really good place for foam. In hindsight, I kinda wish I poured in a denser 2-part foam (not flotation foam) that added some structural stiffness, but that would have slowed the build down at the time and I just wanted to get it on the water.

Skip the pvc. If you think you need a support, add one using whatever you core your deck with. Epoxy doesn’t stick to pvc.

Nate


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## DuckNut (Apr 3, 2009)

Emerald Shiner said:


> If you are re-building a boat then it wasn’t done correctly the first time. If the foam is waterlogged then they used the wrong foam.







































I digress
https://www.thehulltruth.com/boating-forum/247338-your-flotation-foam-may-not-float.html


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## JPizzle (Nov 9, 2017)

I found this on a website in regards to the US Composites two part foams. I think you could say both sides are correct. The foam doesn’t necessarily soak up water, yet any water that gets into a sealed place and has no where to go, is essentially submerging the foam in the water in the compartment.



_14. *Is this foam water resistant?*

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case will all after market closed-cell polyurethane foams and even manufacturer installed foams._

I have to bring my trailer to Miami in a week or two to pick up something for a project so I will hit up Polyumac and FGCI then. Until then I will keep on the demo and any planning.


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## Emerald Shiner (Dec 26, 2017)

JPizzle said:


> I found this on a website in regards to the US Composites two part foams. I think you could say both sides are correct. The foam doesn’t necessarily soak up water, yet any water that gets into a sealed place and has no where to go, is essentially submerging the foam in the water in the compartment.
> 
> 
> 
> ...


Exactly my point. If the boat is constructed properly no water should ever touch the foam.


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## DuckNut (Apr 3, 2009)

WhiteDog70810 said:


> Turning the boat over and pouring 2-part foam between the deck supports is a great idea. I wish I did it that way. If you want an excuse to learn to vacuum bag, you can be really fancy and cut the foam off level with the supports and then vacuum bag a layer of glass over the foam to protect it from the day-to-day wear and tear.


Just be aware and careful. If you add too much you can have the foam expand too much and possibly separate the two pieces.


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## DuckNut (Apr 3, 2009)

Emerald Shiner said:


> Exactly my point. If the boat is constructed properly no water should ever touch the foam.


Emerald - we are on the same page and agree in a perfect world the stuff will never come in contact with water.

It all starts when the sun beats down on the sole and the hull is in cold water and condensation starts and all down hill form there.


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## SilentHunter (Jun 14, 2010)

wasting your time with foam in this hull. 

build a floor with stringers, its worth it.

if you plan to do anything bigger than a 15 you will need stringers, the floor will flex to much with a 20/25.

and whoever said to hang a 20inch shaft on this hull is wrong.

15 inch shaft 25 mercury tiller is best for this hull. mine does 30+mph and floats in ankle deep water. make sure theres no hook in your hull, some of the johnsons had a hook in the transom area.


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## JPizzle (Nov 9, 2017)

I don’t think I would be wasting my time with floatation foam for safety. The whole reason I am doing this boat is for me to have something easy to take my young kids on and for something for them to drive when they get older.

And I have no intention to put in stringers or a false floor. I am leaving the middle bench which has the live well. And with the front and back deck having a bulkhead and deck, it should be at least if not stiffer then it was before. I would be fine with a 9.9 or even 15 as I won’t go more than 3-4 miles from a ramp anyways. Anything more involved and we will just use our Pathfinder.


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## Battfisher (Jan 18, 2016)

JPizzle said:


> I have been following this forum for awhile and finally have joined. My name is JP and I live in Naples. I have been wanting a second skiff for quick fishing trips in the shallow 10k as opposed to using my bayboat. I saw an old beat up johnsen skiff while in Ocala and thought that would make a great little skiff with a front and back deck.
> 
> A quick google search showed me that I wasn't the only one who had this idea. I could easily just go buy a saltmarsh and be done with it, but I have that itch to rebuild one, and really dont want something too nice since it will get minimal use. After two years of looking, one popped up locally and I had to buy it.
> 
> ...


I used CL Mattson out of Tampa to build the platform for my previous 14' skiff. It was transom mounted and worked great - I had my transom rebuilt prior to the install and it was solid as a rock, so I had no concerns with the loads from the platform. Had it for 4 years. It was my first poling platform so I had it oversized a bit and although it looked a bit funny I never worried about falling off of it. If you go to their website there's a picture of my two sons sitting on the platform while fishing - still my favorite picture of all time.


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## paint it black (Nov 3, 2007)

I had the same exact idea, to rebuild a Johnsen, you can see a thread on it somewhere here in the bragging spots, dated back to 2009. I ended up buying a brand new Ankona and sold the Johnsen to another forum member, so ended up finishing the Johnsen, then sold it and bought an Ankona. It sounds super cool to build one yourself, but when it comes down to it, it will never perform like a skiff designed specifically for fishing and poling shallow water. You have the right idea, Polyumac and Joe's FGCI is definitely your best bet for materials. That's where I buy everything for boat builds. We are actually getting ready to flip a highsider back over that we just did a full overhaul on. Dragged it out of a buddy's yard that was going to send it to the dump, a four week overhaul and its ready to hit the water. Oh yeah, I would definitely close up the foamed sections.


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## JPizzle (Nov 9, 2017)

Paint it black, I know it doesn't make sense. I have run the numbers and won't really be saving anything. I am more doing it because I want to. This one is small enough that it isn't that involved and will get it out of my system and not take forever. My kids are already excited about fixing it up even though they won't do any of the actual work. 

And I'm all honesty, a Jon boat would probably do what I want this to do at a less expensive price and be easier but it isn't what I want.


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## Philip (Jan 6, 2018)

SilentHunter said:


> wasting your time with foam in this hull.
> 
> build a floor with stringers, its worth it.
> 
> ...


What do you mean by "make sure theres no hook in your hull, some of the johnsens had a hook in the transom?" What would a hook in the transom mean?


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## WhiteDog70810 (May 6, 2008)

Rocker is when the bottom of the hull is convex, like a rocking chair rocker. Most power hulls have some rocker toward the bow to improve the boat’s manners under power. Hook is the opposite; some part of the bottom of the hull is concave. This is generally considered a bad thing and often happened in the middle of old wood hulls as the wood broke down, but some planing hulls had a ramp built in to the last 1-1.5’ toward the stern to lift the stern (like permanent, non-adjustable trim tabs). Sometimes it is intentional; sometimes it is sloppy fairing that is played off as intentional. It was very common back when folks were converting displacement hulls to planing hulls; adding hook added lift to the stern that would otherwise want to suck down under power. Some folks swear it helps performance; other folks say it is a half-assed way to fix a bad hull design. The truth depends on your perspective.

Nate


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## JPizzle (Nov 9, 2017)

I have read a lot of old threads and can’t figure out what is the best transom height to put back in. One side of me wants to not have the notch, and use a TH mini-jacker or just have the transom step up. Seems like the 20” shaft would give me some more freeboard with out the notch, and put the engine at a higher level for the driving the tiller. I can’t think the weight difference would be that much.


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## JPizzle (Nov 9, 2017)

Have been busy lately but made a little progress.

Last week I went to Polyumac and picked up 3 sheet of 1/2" aircell for decks and a sheet of their gatorboard for the transom.

Then went to FGCI and got a roll of 1708, 4 gallons of poly resin (probably need more), two quarts of desert ran brush able gelcoat, two pails of fumed silica and a bunch of misc buckets, rollers and other tools. 

Last night I cut the old transom out. The inner core had some water damage but really not that bad. Looks like a second layer of plywood was put in the inside and then covered over with matt, along with a small piece on the outside. Was able to get it all off with out too much damage except for one area.






























I have some cleaning up to do around the edges. I was using my grinder with a concrete blade as I couldn't find my grinder wrench and wanted to get it done last night. I figured the best to get the edges would be a abrasive disc to cut the heavy material and then a flap disc to smooth it out. 

My next step is to get the transom back together followed by sanding inside and out. I had planned to get 3/4" gatorboard to double up for the transom, but the guy at Polumac told me the 1/2" would be sufficient doubled up. Should I stick with a 1" core or try to get to 1.5". I also have more than enough biax so i could just do an extra layer more than what I originally planned.

Also need to nail down transom height. I feel like I want a 20" shaft motor, but very well could end up with a 15" if I find a good deal on one. Would putting the transom flat across the top, minus the notch down, which would put me at 18" be a bad idea? I figured I could get the TH marine bracket which I could mount a little low, and with the setback the 15" would work?


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## permitchaser (Aug 26, 2013)

Man I can't wait to see what you do with that boat


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## Wellcraft (Mar 23, 2017)

Following


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## JPizzle (Nov 9, 2017)

Finally getting back to the boat. Having twins and some remodeling at the house takes away from this project.

Need to get the transom core cut and need to finalize a height. Would putting the transom flat across the top, minus the notch down, which would put me at 18" be a bad idea? I figured I could get the TH marine bracket which I could mount a little low, and with the setback the 15" would work? Or raise up the bracket for the 20" shaft. This would just give me a little more transom height to keep any water out.


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## Guest (Jul 30, 2018)

I would lock down a motor length first. If you go with your plan, the jackplate might not have enough setback with a 15” motor to allow full tilt. I like to stand and drive so I tend to build 20” transoms, it allows for me to stand and drive and not have to crawl on my knees to shift the motor. It also puts the tiller at a better angle for me. Again, before anyone says I am wrong... this is how I set them up for myself and my comfort!


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## yobata (Jul 14, 2015)

JPizzle said:


> Finally getting back to the boat. Having twins and some remodeling at the house takes away from this project.
> 
> Need to get the transom core cut and need to finalize a height. Would putting the transom flat across the top, minus the notch down, which would put me at 18" be a bad idea? I figured I could get the TH marine bracket which I could mount a little low, and with the setback the 15" would work? Or raise up the bracket for the 20" shaft. This would just give me a little more transom height to keep any water out.


If I were to do my build again and have the option, I would have gone with a 20" transom and a 20" shaft motor. If you slow down very quickly off plane, the wake will come over the transom (easily mitigated by slowing down slowly)


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## JPizzle (Nov 9, 2017)

I agree and that is why I was thinking the taller transom. I just didnt know if it was worth having the transom bump up, or just be straight across. I seem to remember that most short shaft tillers were about 17.5" to cavitation plate. So was thinking I could end up with the option for both.


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## yobata (Jul 14, 2015)

Just remember that the transom on these boats was not plumb vertically (at least on mine it wasn't). I mention this because when you measure 15" or 20" to cut the transom, the board/core will be flat, and when installed at the angle, you lose some of that height thanks to the slant...


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