Foam cored 20 footer?

To core a hull is not ‘plain sailing’ (until now). We previously introduced the option of a ‘homo-medium honeycomb’ skin where the core is a honeycomb of pre-manufactured GRP ribs and channels and attached with GRP tabbing to the inside of the outer skin. The strength of GRP is about 500 xs as strong as foam while the area summation of all cross sections of the honeycomb’s legs is 1/30 of the total skin area (2mm thick @ 60 mm distance). Those figures mean that the GRP legs are 16X + stronger with only 0.6x the weight of (solid) foam. NOW WE ARE TALKING STRENGTH WITH LIGHTNESS! (Never mind the integrity and durability). If the idea appeals to you, we can, under certain pre-conditions disclose the manufacturing procedure of those hollow ribs for your (designed by us) 45 ft yacht. To try the system we can supply you with a flat pack kit of our 30 ft fast cruiser, which will be equipped with hollow ribs. We possess the moulds for those hollow ring ribs and can include those ribs into the kit. I do not try my inventions on a small scale because luck was always with me but understand people for not trusting a piece of paper. We will (in good time) ‘teach’ you how to make a complete GRP skin smooth and without hassles but leave it for now. Too many new ideas may confuse the main issue of the honeycomb. The enclosed attachment do show the main parts but for clarity we omitted the details of stuffing the gaps afterwards with PU foam and ‘glassing the whole inside over. Additions to the ribs such as integrated deck beams etc are left for late

 

The principle sounds a bit like "Strongplank" which is a PVC foam strip, braided with glass and polyester. These strips can be handled just like normal wooden strips, put around a set of stations. Modern day strip planking.
The inner and outer skin are attached by the foam, but also by a huge number of beams, formed by the edges of the strip.

Strongplank is no more, but a new equivalent is "Everstrip", marketed by "Brands Structural Products" in the Netherlands. Same material, different name.

 

Jeroen

a short explanation to previous post

 

Thanks for the clarification, although Herman's description got me to understand what you meant.

Herman:
Thanks for sending me that information package!

 

Hello Jeroen

It seems you are well underway with Herman. My only concern is that you do not see the difference between valuable information and non-essential talking. In your reply to our post, you ‘understood’ what Herman was saying, but he is saying nothing. Nor for your benefit, neither as criticism of our post. Let me give you an example:
Herman’s ‘Strongplank and our concept both are from FGRP and that is where the similarity ends. Let us show you some differences:

1A Strongplank is the starting point in hull planking.
1B our hollow ribs / mono-medium (GRP) honeycomb are applied at the finishing stage.

2A Strongplank’s only benefit were its correcting qualities about fairing of stations, eliminating ‘lofting’ , which is a difficult task for D.I.Y boat builders.
2B our building kits do not need those correcting possibilities because our mathematical input in a computer gives the building frames shape a precision unheard from any other design program. This precision allows us to make the moulds for the hollow ribs, before producing the boat.

3A Strongplank is lengthwise nailed to the building frames giving strength only in that direction
3B Hollow ribs are across with the piece-stringers fitted in-between giving strength in all directions

4A Strongplank are foam-filled (necessary for manufacturing purposes mainly)
4B Hollow ribs AND our longitudinal U-shaped piece-stringers are not foam filled.

5A the required bending of Strongplank limits the cross section and/or wall thickness
5B Ribs being mould formed making the cross section and/or wall thickness as required.

\6A Strongplank comes in 12 mtr lengths. If you need a length of say 9 mtr the other three mtr is waste because it is bad engineering practice to join pieces like one can do with a wooden plank.
6B hollow ribs are mould produced and have, apart from trimming, no waste.

7A Strongplank are ‘planked’ on the outside only and are not a ‘core’ for a sandwich construction.
7B hollow ribs, being of light gauge, are only spacers between outer skin and inner skin making it a true honeycomb with its tremendous strength.

8A Stiff Strongplank cannot be used as longitudinal connecting pieces between the ribs. Its cross-sectional polar moment of inertia prevents it following the ever-changing direction of the skin.
8B our U-shaped (toe-down) stringers are able to twist before tabbing down and thus follow the contour of the skin, make them a perfect basis for the inner skin (completing the honeycomb)

Enough for now and good luck.

Cheers

Marinus

 

Thank you for your kind words.

 

some comments

When you want to build a 20' boat as a practice for the real stuff for the 45 footer, choose a building method and materials which you will also use for the 45' project. No plywood asking me.

In fact this was the easier part and certainly not a lot of work. Per m1 about 30sec. for routing, the same for filling with bog with help of a candybag and maybe 1 min sqeegeeing excess bog. Filling in two or three stages, so a total of 3 min per m1 to get an idea. In addition to this making the bog, which requires most of the time.

Foam has a good track record. Be aware there is a lot of talk about bad quality foam boats, but these are production boats with all kinds of manufacturer failures. As a DIY you can make a perfect, reliable and sound product.

Once I was a woodworker and I've never thought there would be a time I would say: foam is much easier to work with. I don't regret one single moment my choices. In this regard I also don't see the advantage of the strongplank. When you want to do strip building just use bare foam strips. I realize these requires some more laminate than the strongplank strips.

Only downside of foam I see is the high cost, being the most expensive part of the hull structure.

Water and a hollow hull structure (with honeycomb or comparable materials) seems not a good combination to me. An enclosed empty space in the wall of a boat will fill with water, sooner or later.

Henny

 

Thanks for the valuable feedback everyone, it is highly appreciated.

I am now at a point in time where I will have to start costing out the smaller boat project to have an idea what I am up against.

Main requirements that I would like to do foam cored version of the boat, and to infuse as many parts as possible, including the hull.
Since the main purpose of this boat will be to get experience and get a boat to allow me to go sailing it seems to me that I will have three major chunks in my budget:
- materials for the hull (foam, wood and epoxy)
- equipment (infusion needs pump and all kinds of additional consumables)
- fitting out (here I think biggest cost will be the mast and sails)

Am I missing anyting big?
What price range can I expect for a mast? It would need to be able to do some near shore sailing.
I already have a good candidate supplier for most of the foam, epoxy and building equipment. However I am still looking for a good supplier for fitting out equipment (mast, sails mainly).

 

One more question, will it be easier to infuse a round hull than a chined hull?
I would not be surprised if additional consideration for the chines in the infusion strategy is needed.

To be more specific, I'm currently thinking about these two designs:
http://dixdesign.com/didimini.htm
and
http://bateau.com/studyplans/SB18_study.htm?prod=SB18

I think I will go for the SB18 even though I like the Dix more for the following reasons:
- cheaper to build (I think)
- trailerable
- smaller

However the infusion of the hull due to the chines worry me a bit.
I do not know if chines and foam are good friends?

 

Both have there own pro's and con's. Main difference with infusion is that the chines tend to introduce "trackracing", in other words form a channel through which the resin will travel faster then in other areas. When the resin front is parallel to the chines this is not much of a problem, but in the other direction unexpected surprises can occur. A meticulous way of laying up the dry fabrics can prevent all this. Consider several pieces of fabric with the overlap along the chines. Gives also extra strength to the chines.

Henny