MG20 questions to designer

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Matkuz
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MG20 questions to designer

Post by Matkuz »

Hello, I have finally finished my last project so i can start with MG20.I've got some questions.First one, because of hi prices and lack od plywood in my country, im thinking of making a hybrid, and use foam as a core for side panels and deck.Is it possible to get foam core lamination schedule ? Second question is about modifications of bottom. What i mean. Is there calculated pattern for adding strakes, chine, reverse chine to this specific hull ? Third question is about pad. I would like to add one and i need help with size of it for this hull. I would like to hang 250hp on 8 or 10inch hydrsulic jack plate.
Thank you very much :D

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Re: MG20 questions to designer

Post by Jeff »

MatKuz, The designer, Jacques Mertens-Goossens, is away on a vacation. He is also retired and not sure when you will get a response!! Sorry, Jeff

Matkuz
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Re: MG20 questions to designer

Post by Matkuz »

Thank You Jeff, I'll wait, may be i'll get some info

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Re: MG20 questions to designer

Post by TomW1 »

Matkuz, what is the difference between plywood and foam? Normally foam is 3 times more expensive than plywood to use due to the need to use extra fiberglass and epoxy plus the cost of the foam itself. Once Jacques gets back to you why don't you price out both materials and see which one is cheaper.

As far as the strakes again I believe the plan will show where they should go, all the drawings in the study plans have them. It will be up to you whether you add reverse chines or spray rails. Jacques does not favor pads so do not know what he wiill say on that subject. So go ahead and buy the plans some of your questions will be answered in them, then come back and ask all you want. All of us will try to help you any way we can.

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BarraMan
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Re: MG20 questions to designer

Post by BarraMan »

As far as the strakes again I believe the plan will show where they should go, all the drawings in the study plans have them. It will be up to you whether you add reverse chines or spray rails. Jacques does not favor pads so do not know what he wiill say on that subject.

My Mangusta plans are pretty vague on strakes. I spent a lot of time pondering strakes before I built mine.

Jacques makes some comments on strakes here: viewtopic.php?t=63623

I also make some comments on the strakes and reverse chines on my Mangusta-based hull in my build thread:

JM's plan's are fairly basic compared to some other designers but deliver a well designed hull (or we assume so). Then some of us at least do stuff to it that we think will suit or application.
In my case, after looking at lots of other similar hulls and reading a bit, I put reverse chines on my hull. They are not on Jacques plans. I suspect JM would say that the hull doesn't need them, and he is probably right.
If you look back to some early questions in my build you will see that I was concerned about strakes - what shape, how many etc. The plans give very little detail just a couple of lines indicating where you might put strakes. JM told me that the hull didn't need them anyway. Because I wanted to have the stringers sit over the bunks on the trailer, I only put one strake either side on my hull. They are fairly "aggressive" - triangle in cross-section.

Image
Image
Image

So how did it all work? Well, I can put the hull on the plane in about a boat length with a burst of power, or if I let it come up slowly it will do so around 15 kts. It corners like its on rails - if I pull it into a tight turn at speed (>30 kts) and feed the power in I can just get it to start to slide, with no obvious vices.
I went to a lot of trouble to make sure the hull was true and square etc to within a couple of mm of tolerance and I put a lot of work into ensuring that the bottom was true and flat, with no hook or rocker.
But of course you have no idea what is going to do until you put it in the water.
I have had it up to 48 kts and it is rock steady at that speed, but its sweet spot for cruising is around 27 kts.


The only other Mangusta hull that is documented on this forum is by "fmiles". He posted on strakes on a thread I had under the name "LeeFitz". He complained that his was a 'wet' boat, so I went a bit more aggressive with my stray rail/stakes - the result being my boat is dry except under the most difficult of conditions.
Last edited by BarraMan on Sun Apr 09, 2023 9:18 pm, edited 3 times in total.

Matkuz
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Re: MG20 questions to designer

Post by Matkuz »

TomW1 wrote: Wed Apr 05, 2023 10:08 pm Matkuz, what is the difference between plywood and foam? Normally foam is 3 times more expensive than plywood to use due to the need to use extra fiberglass and epoxy plus the cost of the foam itself. Once Jacques gets back to you why don't you price out both materials and see which one is cheaper.

As far as the strakes again I believe the plan will show where they should go, all the drawings in the study plans have them. It will be up to you whether you add reverse chines or spray rails. Jacques does not favor pads so do not know what he wiill say on that subject. So go ahead and buy the plans some of your questions will be answered in them, then come back and ask all you want. All of us will try to help you any way we can.

Tom
As i said, nowadays it's harder to get okoume plywood than foam core materials in Poland, and prices are quite similar. Especially for private boat builder. The other think is that its easier to work with foam in my opinion, its easier to cut and easier to form. Im rooke but ive build few things with foam core, and i think its quite nice to worki with.

i've already buy Mg plans and as BarraMan said, those plans are not so clearly about adding lifting strakes or reverse chine/spray rail. That's why im asking :)

BarraMan, could you give an example of dimensions of your strikes and reverse chine ? I've got photo of your transom and they look quite sharp. :)

Thanks a lot for your respond guys! :D

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Re: MG20 questions to designer

Post by OneWayTraffic »

Since the unfortunate passing of the designer you might be a bit on your own with respect to modifying the design for foam. There have been some posts on here by it, and the designer was working on a foam cored manual: I'm not sure what the status of it is. But there are a lot of resources online if you look.

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rick berrey
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Re: MG20 questions to designer

Post by rick berrey »

cold mold = cm
single fiberglass skin = SFGS
Formulas , cold mold plywood to foam sandwich
A. 1 CM to .66 SFGS , B. SFGS x 2 = core thickness , C. 0.7 of SFGS = total fiberglass laminate
Using two 1/4" cm plywood skins , equaling 1/2" plus the glue and the fiberglass hull cover of say 1/16" , which gives 0.25 + 0.25 + 0.062 = 0.562" of CM
(A) Ratio 1to 0.66 or 0.562 x .0.66 = 0.371 " SFGS
(B) 0.371 x 2 = 0.742 or 5/8" or 3/4" core thickness
(C) 0.7 x 0.371 = 0.259 total lamination,s thickness
0.259 divided into 2 surfaces = 0. 129" of fiberglass lamination per side
Book , Foam Fiberglass Sandwich construction by Ed Horstman , Tri - Star Trimarans would be recommended if you are doing a foam build . I would convert the material , make a list and then calculate the weight of both the wood build and the foam core build to see if the foam build is an option .

fallguy1000
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Re: MG20 questions to designer

Post by fallguy1000 »

I would be glad to offer any advice to detailed questions after you understand foam costs more and takes longer.

But not going down the rabbit hole if you think it is cheaper..
My boat build is here -------->

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Re: MG20 questions to designer

Post by Jaysen »

I think it’s worth noting that the OP specifically stated “at this time” on the cheaper front. Consider his statements.
1. In Poland. There’s a war on his border hampering supplies of some products.
2. He has more availability of foam as marine ply is reserved for pro builders.
3. He has experience using it in other projects.

Under normal conditions I think we would all say “avoid foam”. But these are not normal conditions and we should answer the question if we have the answers. I do not. I just think we are being a bit less helpful than we could be given the unique circumstances here.
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