Jamie Mantzel's Fiberglass Pontoon/Catamaran Fiberglass Boat Design

Hey everyone, what do you guys all think about Jamie' Mantzel's simple fiberglass boat design he used to make a 30 foot pontoon/catamaran solar powered boat? He posted about 90 videos on youtube detailing the step by step process of building the boat. I want to use the same technique to build a 40'-45' cruising catamaran, do you think it would work?

Briefly, his technique is:

1. Make 2 flat sheets of fiberglass 6' x 15'
2. Cut the 2 flat sheets and attach them together to make a mold for half a pontoon/hull that is very narrow and aerodynamic with a thin, pointy nose
3. Use the mold to make each half of the pontoon/hull with fiberglass and polyester resin

He built this essentially by himself in the jungles of Panama, it's pretty amazing. He doesn't use any foam to my knowledge since he wants a heavy duty boat for hauling construction materials.

The final product turned out fantastic and he shows video of him testing the boat and it seems like it worked great, but I wonder if the same technique would work to make a bigger, cruising catamaran

I want to use the same process but make them a little bigger:

1. Make 2 flat sheets of fiberglass 10' x 23'
2. Cut the sheets and attach them to make a mold for half the pontoon/hull
3. Use the mold to make each half of the hull with fiberglass/polyester resin
4. Maybe add foam core??

For those of you who have never seen the videos (it's a must watch!!!), here is the youtube playlist link:



Also Jamie, if you ever see this, thank you SOOO much for posting videos of your construction process!!

 

Right, well, "old mate" seems to be brainstorming himself there, I'm not sure why he elected to make his "mould" out of fibreglass, when using his methodology, the metal sheet he was laminating on, would have had a better chance of being formable. As I read it, he intends to bend the sheet in a "U" shape, and pinch one end closed, to form both the bow end, and stern end. You won't do that with a sheet of GRP, it will just bust at the pointy end. He might have done it with sheet metal, though. However, the shape obtained, might leave a lot to be desired, especially for a sail catamaran, where the ability to tack in a timely manner, is likely to be lost. And don't start me on the extra hull jammed in between ! He can't be serious, as John MacEnroe would say. I'd suggest you experiment with a sheet of paper to better appreciate what you get, shape-wise, with a sheet of metal, all you'd get with GRP is an expensive cracking sound.

 

Thanks for your reply and input, I really appreciate it!

I thought I had posted a youtube play list link, but I guess only the first video in the series shows up. Here are some additional videos showing him successfully building the mould:



And this is the video tour after the boat is constructed:





I'm not sure why he made the mould out of fiberglass and not the sheet metal, but he doesn't bend the sheet in a "U" shape, what he did was he joined two flat sheets of single layer fiberglass and connected them in a way to make an aerodynamic hull. It's hard to describe in words, but if you watch the later videos in the series, he shows exactly how he does it. If you search youtube for "J Mantzel" and go to his play lists, look for "shark slicer" and that is the playlist that has 90 videos showing every step of the process of building the boat. There's videos showing him driving the boat and it seems the shape of the hull is pretty darn efficient and aerodynamic. He didn't end up making the extra hull jammed in between haha too bad i would have loved to see if it would have worked.

I'm thinking of using this design because it's so simple for a power catamaran rather than a sailing catamaran. To be honest, I don't have much experience boat building and this is one of the few designs that's freely available with very detailed youtube videos, which is why I'm interested in following it. If anyone knows any other good designs with detailed videos, I would be very interested as well. I want to avoid using wood as much as possible due to the maintenance issues.

 

Oh now I remember why he didn't use the metal sheet for the mould, he only had a metal sheet that was 2' x 15', so what he did was he made a 2'x15 single sheet of fiberglass on it, moved it over, made another 2'x15' sheet of fiberglass on it and joined them together and moved that over and made another for a total of 6'x15'. He essentially built this boat alone in the jungle of panama so he was limited with supplies.

 

That bloke is a "bush handyman" type, and I couldn't really get the gist from watching the second video, but I would not have any confidence in that method producing something that isn't "rough as guts". A 40-45 foot boat of any kind, represents a considerable investment in money and time, and you want the result to have full utility, and to be a realiseable asset, if need be. I don't see this method satisfying the first requirement completely, or the second requirement at all. What exactly are you looking to have, a motor catamaran, for use where ?

 

Mario, this comment "hull that is very narrow and aerodynamic with a thin, pointy nose" is totally at odds with "I want to use the same technique to build a 40'-45' cruising catamaran" - the two are basically incompatible in the real world.
If you want to live with even just the basics of some comfort on a 40' 'cruising' cat, then very skinny hulls are not the way to go.

If you want to build a power cat, there are plenty of excellent designs out there that have much more suitable hull shapes - have a look at Richard Wood's Skoota designs for example -
Sailing Catamarans - First Choose a Design http://sailingcatamarans.com/index.php/designs-2/6-powercats

 

Another problem with the "bodgie" mould technique as outlined, was the symmetrical ends, the stern the same as the bow, not the best idea to keep pitching motions down.

 

Thanks for the reply and input! When you say that it's not compatible, is that just from a comfort aspect? Or are there other reasons why you wouldn't want skinny hulls? I was thinking of making the hulls around 4.5 ft, to be honest I have no problem with sacrificing comfort for improved aerodynamics. However if there are other reasons why I should avoid skinny hulls, please let me know!

Also thanks for the link, I am checking it out now!

 

I think you need to specify what you want, speed, area of operation, type of power, and other things. A "jury rigged" mould is likely more a handicap than a help.

 

I am looking for something for coastal cruising that I can put solar panels and a watermaker, where I can go camping/fishing with my family for a week or so at a time and be as self sufficient as possible. I don't mind the skinny hulls because my kids can sleep there and I can sleep on the bridge deck. I don't care too much about going fast.

I agree about the symmetrical ends not being ideal, I was thinking of making the back end a little wider.

I like this design because it's so simple and the videos he puts out are very detailed. Yeah, with the videos I posted, it's hard to understand everything going on without watching all the previous videos in sequential order. But if you watch the final video where he gives a tour of the final product, it's a bit easier to understand.

I feel like that if you made the boat out of (many layers of) fiberglass, it would be very reliable and strong. The only concern I have with this technique is how aerodynamic the hull would be. I personally think it would be pretty darn aerodynamic (and it seems that way in the videos that he posted where he actually tests it). Other than the fact that it might not be as aerodynamic, what other reasons specifically that you don't think this would be a reliable asset? I'm not trying to be difficult, just trying to get a better understanding. Thanks again for your time and input, it's very much appreciated!

 

Mario, everybody would love to have skinny hulls - they have everything going for them, same as people would love to be skinny themselves.
However - you say that you want creature comforts like a water maker, solar panels, nice accommodation, lots of essential equipment - and all of this adds up to form WEIGHT.
And weight is the killer for skinny hulls - you need buoyancy (ie volume) in the hulls to support all that weight.
Have you heard about Archimedes? He was a boss philosopher who cottoned on that an object floating in water displaces the weight of the water that the object 'pushes aside' when it is afloat.
Archimedes' principle - Wikipedia https://en.wikipedia.org/wiki/Archimedes%27_principle
Load up a hull that has not got enough buoyancy, and your skinny hulls will increase their draft rapidly - if you don't do an accurate weights tally on your skinny cat as you build it, you might well find that it floats with the deck awash the first time you launch it. I have seen this happen a couple of times here with home built boats.
I think that the lad in the video mentioned that the fibreglass materials cost him $5,000 (?) - you can have a crappy hull shape and you can have a good hull shape, and the odds are they will both require the same amount of materials (and hence the same cost of materials) - so it makes sense surely to start off with a well proven and 'good' hull shape, doesn't it?
And in my opinion, any set of plans that you buy from a reputable designer will have a much better hull shape than the one in the video.
Take note of the number of 'hits' this lad gets for his videos - I think he makes good beer money from Youtube out of this endeavour.

 

Thanks Bajansailor, that was super helpful! I would like solar panels, water maker, but I don't need "nice" accommodations and just the barest essentials of essential equipment, but your point about weight is well taken. Also I'm not convinced that it's such a "crappy" hull shape, since he actually shows video of the boat "slicing" through the water:



What do you guys think of that video? It seems pretty efficient to me, but I'm not an expert!

 

Also to deal with the weight issues, my other thought was to make it a trimaran with 3 hulls

 

I am not saying that the hull shape in the video is crappy - yes, she does slice through the water nicely.
However there is no 'perfect' design - everything is a compromise - and this one carries a disadvantage of limited load carrying (and dare I say it, seaworthiness) in favour of low wake / resistance.
I don't think it will perform as well once you load it up with even just the basic essentials required for living on board.
And re that $5,000 of glassfibre materials used - if the hull structure was properly designed, you could probably make those materials go further with efficient design.
Be aware also that a plywood / epoxy hull will generally be lighter than a single skin fibreglass hull, for the same hull form.
Hence why I posted the links to Richard's power cats - you can be assured that he has removed all superfluous weight and designed the structure as efficiently as possible, as he knows all too well that weight kill cats.
The cat in the video performs well in flat water - pretty much any type of boat will do ok in flat water - but what will it be like in rougher conditions, eg where the waves are perhaps 3' high (which is not 'rough' by any means)? I don't think it will be very happy.

 

I went to youtube and watched some more videos of Jamie's "method". and I am not finding myself converted to the cause, , it looks like a great way to end up with something that will look good on a very dark night ! I actually am quite interested in the idea of a motor cat based on two moulded GRP symmetrical hulls, ( only one mould needed) with the rest of it made from frames and sheet materials, and the only thing beside those hulls needing to be strictly watertight, the roof of the habitable space. But I would take the trouble to make a decent mould for the demihulls, not fling something together that looks like a short cut, but really isn't.