Barrelback runabout in Fibreglass foam sandwich

[dantesta]

Hi Fellow boat builders

Need advice on Fibreglass foam core boat building!
I’m embarking on building a Ken Hankinson designed Barrelback 19 foot hacker style runabout.
For all you traditionalists I’ll apologise in advance – I’m planning to build the hull in fibreglass foam sandwich. Here are my reasons why:
1. I live in Australia and the price for good Marine Ply/timber and epoxy is outrageous
2. The boat will be used by my extended family and I don’t want the beautiful timber bright-work dinged when being taken in and out of my boat house or smacked against the dock – It’s easier to bog up a glass hull then trying to fix a timber finish.
I have built in fibreglass before but I’m not an expert and not had much experience in foam core. The Hankinson plans are for ply/epoxy construction but I plan to build in foam core - male mould using Hankinson plans, stitch/ fasten the foam sheets and then glass over using Vinyl ester (not epoxy).
Can someone give me some advice on?
1. What Layup schedule I should consider both inside and out – I want the boat relatively light but strong enough as it will have a V8 powering it. The local fibreglass/foam suppliers won’t give me any help here as they are worried that if they give advice and the hull turns out to be a unsound that they will get sued
2. Advice on the type of foam sheet to use – I’m considering Divinycell range of polymer foam cores or similar. What thickness, fastening tricks, best way to lay up to get the best possible foam to fibreglass bond, steps to avoid de lamination.
3. Whatever other advice you can give! And any good web sites to visit
Cheers
Dan

[PAR]

You need to have a laminate and core schedule worked out for you by a professional. Sandwich structures need a good bit of engineering effort to preform properly.

[dantesta]

Hi Par - yep done this - well spoke to a professional and he wanted a few grand to spec it out - but will try someone else

[Highwater]

I want to do the same thing, but a 12' planing dinghy. Foam sandwich plans seem to be rare for smaller boats. I don't know why. I am going to ask a boatbuilder for advice, but it is a risk.

[Rick Willoughby]

If done well you will have a good boat.

Are you only after free advice or are you prepared to pay for good advice and engineered detail?

There are quite a few builds going on with sandwich panel construction.

This one uses factory made panels:
My little piece of peace

This one has home built panels:
http://www.adventuresofgreg.com/HPB/HPBmain.html

Making your own panels requires decent workshop space with a sizable flat table. You will not get a consistent bond without applying pressure, usually using vacuum. It is also wise to institute basic quality control on the panel layups if you want confidence in the end result. Likewise with the rest of the build.

Rick W

[dantesta]

A fellow aussie I see

I'm prepared to pay for the advice/design but not half the cost of the hull! - I want sound advice not an iron clad guarantee or warranty!.

I'm now preparing some test layups and get a few sheets of foam and some resin/CSM and WR and set up a part male mold and lay it up to find the best layupo to weight ratio and in the meantime get advice from forums like this

Cheers
Dan

[Rick Willoughby]

Dan
You will essentially get free opinions here and you take them or leave them.

If you pay for professional advice it has to be given with a level of assurance. There is an implied warranty or obligation that the professional cannot avoid.

I tried to send you a private message but you have not enabled that function.

If you email me I may be able to give you a free suggestion. (right click on my name above for the address)

Rick W

[tunnels]

Ok foam construction for a semi flat bottom and curved topside at the aft end and a flare it the front . Building over wooden frames ??

20 mm hi density in the bottom and a medium density
in the top sides 15 MM Thickness would do and be resonably easy to bend into shapes
once you get to the curved areas change to 10mm plus a 5 mm layer so it will bend even easyer to form you barrel back and the flare in the front . Dont stick them together but make sure you are able to get the inner sheet out later when you turn the hull over to glass the inside and at that time you can stick them with glass and resin to join and vac them together with a peel ply to help make the inside clean and smooth . Have done this a few times and it can work well just think ahead and plan what will happen later .
Id be getting away from using woven roving and going to double bias glass as well . To get the over laps on the chine right glass the top sides first and round the chine corner onto the bottom ,them glass the bottom round the corner onto the topsides so you have a strong and reasonably thick chine . with the glass laps the right way !! I can not enphsize the use of peel ply enough when doing this type of work as you can see straight away if the hull and its panels are smooth and not limpy and bumpy and you will have got rid pf any surplus resin and once you peel then have a totally clean surface to trowl a coat of fairing compound over without any grinding and dust etc .
The cost of the peel ply and its advantages far outway the exspence involved Believe me !!

[dantesta]

Thanks Mate

Appreciate the reply.

I've hand fibreglassed over a male mold before in the traditional way and got a fairly good finish with minimal bog and sanding -but have not done a relatively big layup as this.

I have to learn more about vacuum bagging - bit of a mystery to me at the moment! I was actually thinking of doing it all by hand layup

I'm thinking of single skin FG on the bottom (due to the flatness of the bottom worried about delamination in foam bottom) and foam sides Any idea of the Layup? - My clac's are as follows:

Bottom Single Skin:
600 X 4 CSM
324 X 3 WR (Bia cloth?)

Sides (Outside)
600 X 2 CSM
324 X 1 WR (Bia cloth?)

Sides (Inside)
450 X 2 CSM
324 X 1 WR (Bia cloth?)

What do you think about Polyester V's Vynalester?

Appreciate any help

Cheers
Dan

[apex1]

Originally Posted by dantesta

Thanks Mate

What do you think about Polyester V's Vynalester?

Appreciate any help

Cheers
Dan

Just a comment: chopped strand mat does NOTHING to improve the strength of your layup !!!!!!!!!!!!!!
It is a nice layer between fabrics or uni / multi dir. layers, but not thought to make 70% of the composite!

Regards
Richard

[Simon B]

Dear Dantesta,
I read your query with interest. I built in 1976, a 53 Foot Yawl in Foam sandwich GRP. In those days it was Polyester resin. She is still afloat with no signs of deterioration of the laminate or any dalamination. We used Derek Kelsall as an advisor and he was quite reasonable as a consultant, then. Obviously I have no idea of what he charges now. I believe he lives in NZ now. I believe he has moved on from the basic method that we used. We had the advantage of there being another yacht of the same design built in foam sandwich so we had a good idea of the laminating schedule from that.

I think that within reason you don't have to worry too much about the laminating schedule. If you overbuild a bit, with a V8 engine it won't matter too much. The main areas for attention, in my view, are high stress areas. In these we linked the skins and then filled with the foam (Airex, 25mm thick) and then laminated on to of that.

Our external schedule consisted of 7 laminates:

1 1/2 oz chopped stand mat (csm) bonded to the foam

heavy uni-directional woven roving for and aft (18 oz from memory)

1 1/2 oz csm to help bond the uni to the csm

then another heavy uni (across the boat)

1 1/2 oz csm to aid bonding and to increase point loading performance

Heavy uni fore and aft

1 1/2 oz csm on top, again to improve impact resistance

Internal was :

1 1/2 oz csm
Heavy uni fore and aft
1 1/2 csm
heavy uni across the boat
When laminating we took all the fore and aft Uni over the forefoot and down the other side. I.e. all the bow area was doubled in thickness. Ditto all high stress areas.

I think you will need to focus on cleat areas, engine mounts, windlasses, towing posts and winches and generally any area that will have a large forces applied for consistent periods.
We did not do any vacuum bagging. The basic laminate was easily strong enough and we wern't worried if the hull came in 1/2 a ton heavier. After all we have 8 ton of internal lead keel. All single skin laminate in this area!

The foam is not good at compression i.e. skin fittings done up tight, so we cut out the foam, linked the skins and then put in compression pads.
Likewise for chainplates and deck fittings.

It is a great method but is more labour intensive with regard to the finishing.
We spent hours with long-boards fairing the hull to a v. high finish. Then, in those days we used two pot polyurethene to paint the hull. I believe epoxy is much better now for protection etc

Good luck

Simon B

[rwatson]

Just been through the layup techniques using DIAB foam.

As someone said before, CSM adds weight, but not much strength. To get a good bond, you can use resin rich CSM against the foam OR, in the case of DIAB they sell a special joining compound (Dyvilette) that can glue the foam sheets together, make a good bond to the foam, fill in grooves or shaping cuts.

Its advantage is that it is very light, and sands at about the same consistancy for foam - so you can do your fairing without digging into the soft foam.

Downsides - I had to buy a big bucket of the stuff to try out - costs AU$333, but I won't have all that extra weight, which is one of the big reasons I am using foam in the first place.