Plastic Hunter Crack Repair

By now everyone is aware that the thermoplastic JY15, Hunter 146, 170, & 216 are all prone to cracking. A few weeks ago I purchased a 2004 Hunter 216 that had a small 6” crack at the bottom of the companionway and a large (aprox. 3’ long) crack from the mast step to the port side rail on the cabin top. This crack on the cabin top seems to be a common place for the 216 to crack as every one I looked at had this crack. I bought the boat for next to nothing and was determined to repair the boat. My first stop was this forum and now I’d like to share my experience in how I went about repairing the cracks on my 216.

I have learned from the forum and from seeing repairs in person on 216’s and JY15’s that the regular fiberglass boat repair method of epoxy & fiberglass is NOT the way to go as the thermodynamics of epoxy is different from the thermodynamics of the plastic hull meaning the epoxy and the plastic hull will expand and contract at different rates and at some point, the repair will crack again. After reading many posts, I was ready to choose between the tried-and-true method of Plexus and a newer product called West System G-Flex. Before pulling the trigger, I wanted to make sure I wasn’t overlooking any repair option. I took a step back, left the “boat” part behind and thought “how do I repair plastic” and that’s when I came across what auto shops, ATV, and motorcycle guys have known all along – plastic welding.

These boats are made from BASF Plastics product called Luran S which is a thermoplastic Acrylonitrile-styrene-acrylate or ASA. Many people refer to the plastic as ABS which is incorrect. They are both styrene based, but ASA is more resistant to temperature changes than ABS. I found a company that specialized in plastic repair products called www.polyvance.com and reached out to them about my repair. They were very knowledgeable, helpful, and friendly and set me up with a Mini-welder model 7 along with some ASA welding rod. I think I spent $200 for both.

To complete the repair, I dremmeled out the crack, then used the welder to heat up the edges of the crack. The ASA welding rod is then inserted into the welder and comes out like a hot glue gun. I made sure the crack walls were still tacky to ensure a good bond with the ASA rod with the base material. I then used the welder like an iron to smooth out the repair and further ensure the repair was well bonded to the base material. You can sand it as soon as it cools, but I came back the next day and hit it with 100, then 220 grit sand paper. It can use some body filler, a good sanding, and some paint, but right now I am thrilled with how the repair came out! I’ll keep you updated on the repairs hold up long term. I have attached some pictures of the small companionway crack I repaired. The repairs are super strong, I can push on it, bang on it and it feels like any other spot on the boat!

 

Short term update: after only a week, the large crack repair on the cabin top has cracked again! A little upset, but it’s a learning process. My boat suffered bow damage just like the boat in the hunter ACP repair manual (https://sbo.sailboatowners.com/downloads/Hunter_216_65456361.pdf) that was repaired with Plexus & fiberglass so I think that will be what I try next for the cabin top crack repair. I was told the repair was done years ago and has held up nicely so I’m confident this will work out well.

My guess why the repair cracked after only less than a week is that I didn’t dremmel out enough of the crack and the weld didn’t have enough material to bond to. I will dremmel the crack and weld again, only this time I’ll also grind down the area about an inch or so on both sides of the crack then fill with fiberglass wetted out with Plexus. I’ll be ordering the real Plexus form Jamestown Distributes and not using the $4.00 Walmart junk.

 

@H216sailor , nice research and writeup.

I've always wondered why the APC breaks where it does. Is the boat under some stress there? This is important because APC is in fact a 3-D LAMINATED structure (Luran-foam-fiberglass), and like all laminated structures gains strength from the layers being mechanically attached to each other. Any ask any ocean racer their biggest fear, and its the boats core delaminating from the carbon skins. Gluing the Luran crack closed does nothing to address the (weakened) laminated structure. Maybe its no wonder they break again?

 

Correct, the boat is constructed with an outer Plastic skin, an inner fiberglass skin, and then both are joined together with expanding foam core in between the two. On these boats, the foam core is quite thick (over an inch in most places). In “traditional” cored boats, the worry is water intrusion rotting away the inner core leading to delamination and eventual hull failure. On my boat there was no stress on the repair as the boat has been sitting on the trailer since being repaired. No loads applied to the repaired area. Many of the cracks on these boats (146,170,212,216,JY15) are in areas with no loads. The general consensus is it is simply the thermo expansion and contraction of the plastic outer skin. In many cases including mine, there is no damage to the inner foam or inner fiberglass lining so there is no repair needed in these areas.

The simple truth is these boats crack. The thermoplastic outer skin wasn’t such a good idea which is why Hunter went back to a conventional fiberglass hull. Unlike conventional boats, the cracking usually isn’t detrimental to the integrity of the hull. These boats can be repaired easily and continue to be enjoyed for years to come. These boats were never intended for any kind of offshore work whatsoever, but rather a few hour sail in protected waters.

Even when my boat is repaired, I am aware that it will crack again due to thermo expansion and contraction, but I’d like to find a repair that works for me that I’m looking to last at least a year or two.

 

From looking at some videos online, they seem to melt some stainless screen into the existing plastic as reinforcement prior to filling the crack with the plastic welder. Did you do this?



This guy used old milk bottle to make an ugly but functional repair.

 

I did not try this method. I have wire mesh but having already done a first pass at the repair, I’m not sure it will be the best method. There are many different types of plastic. Canoes and kayaks are typically made out of polyethylene which melts at 120c where a Hunter’s Luran S ASA plastic melts at 105c. Having repaired poly in the past, it melts much nicer than ASA and stays molten for a longer period of time making it much nicer and easier to work on. it can also withstand a lot of heat without burning. I am able to adjust the heat on my plastic welder, but ASA plastic is very fussy. It doesn’t like to melt but when it does, it’s quick to burn. You cannot melt the wire mesh into ASA like in those videos on poly kayaks. As for the milk jug video, the clear high density polyethylene has a hard time sticking to anything so I’m not sure how long a repair like that would hold up.

I appreciate the help though. Because the plastics are soo different, I mostly try to stick to ASA or ABS repair videos for insight. I might try the PlastiFix, which is powered ABS plastic & solvent. It works the same way as the plastic welder only it’s a chemical reaction instead of head being applied. I’ll do a test with the plexus and PlastiFix on a small area of the repair. Good news is they are both $25

 

Is there a reason why you are not using the tried and true Plexus adhesive?
I recently purchased a 2005, 216, and there are a number of these crack I want to repair, but unable to find a Plexus distributer in Canada.

 

A few different companies make it, Plexus, is really just methyl acrylate. I've had really good luck with "Locktite" branded methyl acrylate..Home depot sells it...near the epoxy.

 

Thanks very much, I'll check it out.
Happy sailing.

Went to Home Depot, Lowes and Canadian Tire, no luck finding anything with "methyl acrylate", they did have LePage Marine Epoxy and J.B. Weld Marine Epoxy neither of which contains "methyl acrylate", going to call Hunter next business day for guidance.

 

I have done extensive hull repairs on our 170. I found that Devcon DA291 Plastic Welder to be an excellent adhesive for this application. We had to repair the entire backside of the tiller mount and hull seam and used fiberglass material with the Devcon. Just like a normal fiberglass repair, fully saturate the material with the Devcon and lay it on in sheets, smooth with an outer skim coat of more Devcon. The color is close enough to an exact match to not require painting and sands/buffs to a gloss finish.

 

perfectly reasonable.

 

OwenPeter - no reason, I just figured if the base material can be melted and reformed, why not do that. Instead of using adhesive to repair ASA plastic, why not use ASA plastic? with that being said, my plexus is due to arrive tomorrow and I'll be finishing my repair with that plus fiberglass. I went back and re-welded the area with the hot welder paying close attention to really melt the base material before applying new ASA and it came out beautifully. I think I will still grind down the weld plus a little extra on wither side and finish with the plexus. Pictures to follow.

I have used the Devcon plastic welder from Walmart on many different applications with great success. Before I started my repair on the boat I was able to find three of them unopened laying around the house. I decided to use the Devcon and the Mini-welder on scrap pieces of plastic. I found the Devcon to be very strong, but very rigid and not flexible. After putting a little weight on the scrap plastic Devcon weld, it broke along the repair. The plastic weld with the mini-welder was extremely strong, and was able to bend the piece very hard back and forth and no damage came to the weld. it was less of a repair and more of a re-molding back together. I'm not saying the boat can flex like how I was treating the practice repairs I made, but these boats are more flexible than a fiberglass boat.

 

My weld has hairline cracks again! going to dremmel out a 3rd time and use the tried-and-true Plexus method. ordered my Plexus from Chembar (https://www.chembar.com/?s=plexus) and shipped to me very quickly. I only bought two of them, I hope that's enough for a 3' long crack.

Any recommendations on what fiberglass to use?

 

First, I want to start by saying thank you for posting this useful information. It is very helpful for the rest of us that play with these little plastic boats.

I am a little curious about the differences in expansion rates between the plastic & standard epoxy for fiberglass. Did you manage to find any actual numbers for those expansion rates? I haven’t found them & I would really like to take a look.

I’ve done some repairs on both my 170 & my 212, which are both ACP hulls. I’ve been using West System epoxy. So far, I have not had any failures of my repairs. The earliest repairs were done this past October (9 months ago). That was a fairly extensive little rebuild, where I glassed in what was left of the motor mount. I basically installed about 30 square inches of ½” thick glass/epoxy & tapered the glass out as I picked up attachment to an area about 4 times that size. You can see pictures of what I did here - https://hunter.sailboatowners.com/mods.php?task=article&mid=11&aid=100114&mn=170 and here - https://hunter.sailboatowners.com/mods.php?task=article&mid=11&aid=100115&mn=170 This boat lives indoors in Florida. It sees temperatures from 60F to around 100F, but probably almost nothing outside that range. That may be a big part of the reason why I have not seen any new problems yet.

Back in the 1980’s, I used a plastic welding system that was similar to what you describe. I used it to repair ABS fairings on motorcycles. It was a very slow & tedious process. I probably only got about an inch per minute, or maybe even a little less, if I wanted to get anything that was close to full structural strength. ...& that was after pre-heat. I never seemed to actually get completely full structural like I could with metal welding. The plastic weld also always seemed more brittle than the material around it. That was one of the main reasons why I chose to try epoxy & glass for repairs on these boats.

I recently had a problem with the rudder mount tearing out of my transom on the 212. I considered going in through the bow side of the transom post rear surface, like what was done in post # 10, but I didn’t want to punch a hole that big into the boat if I could avoid it. Instead, I removed the SS bracket & went in from the back with a 5/8” drill where the pulled-out screw holes were. I then put a blow drier on it for a few days to get everything crispy dry & then filled the holes with rolled up glass & epoxy. After I cut away the excess & filed the new glass studs flush with the skin, my results seemed stronger than new. The original design had about 1” of wood plank behind the skin for the screws to sink into. Now they have about 3” of glass. This repair was recent. I did it right after a 30 mile ocean race. I’ve had the boat outside the inlet probably 5 or 6 times since the repairs were done. So far, nothing seems to be loosening up.

Krylon makes a plastic paint that they call “fusion”. The Fusion White is a pretty close match for the skin on the ACP hulls. Ace Hardware is the only place that I have found that particular paint so far. The big box stores don’t seem to have it.

I will be very interested to hear how your repairs hold up in the long run. If you get the welded seams to stay together, I may try to follow in your footsteps.

Regards,’
Jim

 

If you are just doing a narrow patch, like a v'd out crack, I would probably want to use milled fibers. I would not use cavosil or other fairing fillers or "peanut butter" thickeners. you probably aren't going to have room to use actual cloth unless your V is made at a VERY shallow angle.

 

Hi JimInPB, thanks for the insight on your repair. Here is a link showing the thermal expansion of thermoplastics and fiberglass. I think you'll have less of a problem down in Florida than I'll have up here in CT over the winter. I agree with you that plastic welding just can't seem to get the same strength as the original. my Plexus has arrived and I'll grind out and repair as soon as I find some time to do it. I think I was set on the plastic welding at first because I was on a quest for a permanent repair. I thought if I used the plastic the boat is made out of for the repair, there would be no thermal expansion differences and the repair would last longer. I realize now I am not smarter than everyone and will use the tried-and-true Plexus. The plastic is remarkably easy to work on so even if the repair only lasts 1-3 years, its not really a big problem.

I've been enjoying the boat so far. I've never been a huge fan of swing keels, but a few rubber door stops and not taking a powerboat wake directly on the bow makes for a much more pleasurable ride. I've been trailer sailing the boat as I'm less than a mile from the ramp. The boat is easier than a powerboat to launch and retrieve! She floats like a leaf on the water, literally almost no draft with the board up and rudder out. but the rigging/derigging can be a pain so I think I'll get a slip next year.