New forum member (equivalents in foam to 9mm marine ply?)

[Initial_G]

(and his hopefully soon to be build)

Hi people

Greetings from Belgium, Europe

@ present, havent started any build yet
I did buy 2 sets of plans
- K-Designs KD860 Cat
- Scarab Avalon 9 Tri

I first bought the KD860 plans, but then came accross the Scarab Tri, and decided to build that one (or try to @ least )

Plans call for a plywood 9mm construction
But I came accross PVC Foam info, and figured, lets go with that
Then HDPE (High Density PET) came to my attention...
Choices choices...
Waiting for info on both materials to check what would be best (price/quality) to work with.


So first question (did look on the forum about this but couldnt really find a deff answer):
What are the equivalents in foam to 9mm marine ply?

Thanks

G

 

[gonzo]

They are not really equivalent in any strict sense. These different materials have to be incorporated in the structural design which produce very different results. The plans will have specifications, stick to them. Otherwise, you will need to re-engineer the design.

 

[TANSL]

As rightly said Gonzo, they are not strictly equivalent. In fact, they are not equivalent at all. What you have to look for is a material having mechanical properties that allow it to support, with a certain thickness, efforts supported by the 9 mm thick marine ply.

 

[Initial_G]

Thanks guys

I figured I could go 12mm PVC foam instead of 9mm plywood as Ray's new Scarab 32 can be made in both 9mm ply or 12mm foam
+ I have read a blog someone made that also exchanged 9mm ply for 12mm PVC Foam on a scarab 22

grtz

G

 

[upchurchmr]

So do you have the laminating schedule for the glass on the 12mmPVC foam?

 

[TANSL]

Initial_G, in your first post you said: "What are the equivalents in foam to 9mm marine ply."
From my point of view there is not equivalence. Now substitute marine ply with a laminated sandwich consisting of GRP and a foam core, yes it is possible.

 

[Initial_G]

Initial_G, in your first post you said: "What are the equivalents in foam to 9mm marine ply."
From my point of view there is not equivalence. Now substitute marine ply with a laminated sandwich consisting of GRP and a foam core, yes it is possible.

Hi Tansl

Sorry, english isnt my native tongue
I been reading the forum and it seems PVC Foam has a lot of advantages vs wood ply.
Thats why I wondered if PVC Foam was a better choice to build my tri.

 

[Initial_G]

So do you have the laminating schedule for the glass on the 12mmPVC foam?

Hi Upchurch.

Again sorry for my lack of knowledge in English, but what do u mean?
Already checked with suppliers
Seems Epoxy Resin is highly compatible (read perfect) to work with PVC Foam
So was thinking glass laminating on PVC wouldnt be an issue

 

[TANSL]

Hi Tansl

Sorry, english isnt my native tongue
I been reading the forum and it seems PVC Foam has a lot of advantages vs wood ply.
Thats why I wondered if PVC Foam was a better choice to build my tri.

Nor am fluent in English.
Note that if you change the hull material, you must also change some constructive solutions: union system among floors and frames to shell plates, shape and properties of the longitudinal reinforcements, etc ... So change the material is not to change a certain thickness to another, but change many things.

 

[gonzo]

The construction techniques need to be changed as well. For example, plywood core hulls can have a hard bulkhead attached with no problem. Foam core hulls usually need a more flexible bond, like a layer of foam in between. You can't just substitute materials and build it the same way.

 

[Initial_G]

Thanks for all the replies
Guess it'll be plywood

 

[rwatson]

Thanks for all the replies
Guess it'll be plywood

If you are new to boatbuilding, you will be pleased with your decision,

Do a search on safety with Epoxy to ensure your ultimate comfort

 

[Initial_G]

Next question about plywood

Seems theres 2 woods used: Okoume and meranti

I read that Okoume rotts faster then meranti.
Meranti also seems harder but heavier then okoume

On a 9m boat it seems the overal weight increase would be only around 10%, although the difference in weight between the 2 woodtypes is about 20%

So would Meranti plywood be a good alternative to okoume?

 

[rwatson]

Go lighter ( possibly cheaper )

You're going to epoxy it, if water gets in, they will both rot, if it doesn't, they wont.

Its the structural thing that makes marine ply better.

Dont paint anywhere inside the boat that you dont have to - that way you can see any problems like water coming in from outside.

 

[TANSL]

Initial_G, it is possible that by placing plates in a lighter material, and certainly less strong, you have to put more reinforcements, and stronger. It is therefore difficult to judge whether the okumen will result in a lighter vessel or not and, especially, would be impossible to know the difference.