1208 biax pros n cons..

[86RajunCajun]

Hey all!

What do you guys think of the 1208 biax in place of 1708?

I was considering doing my stringers and transom work with 1208 instead of 1708 because i have read a couple places that it is a LOT easier to mold to the stringers because it is a little lighter. I am a beginner with glass work so i figured if i can get the strength i need out of a couple layers of 1208 and have it be easier to form to the stringers then i may use it instead.

This is my plan..

Fillet and tab the stringers in with 1.5 CSM then go 1208, CSM ,1208 on the stringers.

Then for my transom i plan to tab them in also with the CSM, then lay up the 1208-CSM-1208 CSM-18oz roving to cap it off.

Opinions?

Thanks!
RC

 

[erikgreen]

Re: 1208 biax pros n cons..

It's nice stuff, as you say it's lighter and easier to use.

One thing... are you using epoxy or poly resin?

If you're using epoxy you don't need the CSM (or even the mat on the 1208) and if you're using poly resin you don't need the CSM unless you want to bulk up the thickness of the glass without adding much strength.

Using poly resin you need mat between layers of roving or fabric in order to promote proper distribution of resin and therefore adhesion between layers. 1208 (or 1708) has a stitched layer of mat attached, and therefore you don't need separate mat.

Epoxy is a much better glue than poly, so if you're using that you don't need mat at all, just the stitched biax layer. It can be hard to find biax fabric without the mat though.

As far as strength, the 1208 will work just as well as the 1708. For stringers and transom I'd recommend 3-4 layers of 1208 instead of 3 of 1708 for a generic "small boat" like most of the ones here. Plenty of strength. If you're using a roving layer I don't know if it matters whether it's first or last (ondarvr?) but you will have a nicer surface finish if it's covered.

Tab the stringers in with CSM if you like, but you'll need to make sure you have enough layers of 1208 over that for strength.. the csm is almost worthless in that application. Most of the strength should be applied attaching the stringers to the hull. Use CSM to cover any exposed wood later on.

The thing you want in the end for glass reinforcement work like stringers or transom is a certain tensile strength.. usually whatever you're covering is forming the core of a composite.

This is unlike molding glass to form hulls or hatches... in that case you'd want a certain thickness of glass for stiffness, and usually it's ok to build that up with mat because it's a cheap way to do it.

Erik

 

[86RajunCajun]

Re: 1208 biax pros n cons..

Thanks for the info Erik.

I will be likely using poly resin, but i will have to decide later when i find out what is available local. I refuse to pay $200 in shipping and handling just to get the material to me. What a ripoff!


I plan at least 4 layers of material over the stringers and up to 6 on the transom. I have 150hp Mariner v6 that is gonna hang there <450lbs> so it has to be tough to meet my standards. I am going to use 2" thick transom and some HEFTY knee boards glassed into the stringers and bulkheads. Its going to be all one tied in beastly unit.

The way the boat was build from the factory it only has one layer of biax looking material casing the stringers in and one layer of roving and then biax looking material holding in the transom and kenee boards. I will make it much stronger.

I figured the tabbing would at least held hold the stringers in place while the PL cures and till i get them cased in the biax. The main thing i want is the ease of use. If 1708 will lay nicely and isnt too much of a bear to work with i will use that for the added strength.

Erik, since i have you here lol, i have another question. What material would be best for covering the wooden frame of the helm i am building? I plan to make the frame and secure it to the top cap by glassing it in. Thanks for the info!!

RC

 

[erikgreen]

Re: 1208 biax pros n cons..

Unless you plan to do something unusual with the helm (which I am guessing will be a free standing structure on your deck) then I think almost any cloth would work pretty well. You honestly don't need much strength for the glass skin, since it's probably just going to be for abrasion resistance. So you can use whatever's cheapest/easiest.. the thinner the cloth, the easier it'll be to wrap around corners.

If, on the other hand, you want to use composite construction instead of an internal frame for the structure, I'd recommend forming the panels from 3/8" plywood and covering inside and out with 1208 fabric. Tons of strength, and should be very light and have lots of space inside.

Sounds like you're going to make a super-strong boat. That's the way I like to go too, but a word of caution: Don't let the "more is better" idea run too far.. you can end up with a very heavy boat that way, which will perform poorly and potentially be less safe than a simply well built one.

Feel free to bounce ideas off folks here during the rebuild, that should provide some perspective.

For keeping costs down, I'd strongly recommend either Iboats' epoxies or US Composites (uscomposites.com). Depending on which kit you buy from USC, the epoxy comes delivered at a cost of about $60 a gallon including shipping, or you can get poly from them even cheaper than buying it local, and it's better quality too. They also have fabric, tape, etc.

Erik

PS: One more thing... PL premium needs moisture to cure, and in thicker blobs it can take days or weeks to cure completely. If you want easy stringer bedding, just cut a strip of foam to fit under them and balance them in place till the tabs harden, then glass over it. If you have a good bracing system for the stringers, forget the tabs and go right to glassing them in place with 3 - 4 layers wet on wet.

 

[system-f]

Re: 1208 biax pros n cons..

I'm not sure what your fiberglass supplier is/was, but this topic made me look at the US Composites website prices for 1208. I was very surprised to find it more exepensive than 1708 by almost $2 /yd!

 

[erikgreen]

Re: 1208 biax pros n cons..

Yeah, for certain things they're not so good. Prices also depend on demand, and people like using the lighter fabric because it's easier to follow curves, corners, etc.

For biax fabric and tape with and without mat, I like boatbuilder central.

http://boatbuildercentral.com/products.php?cat=45

They have a forum where if you are planning on buying supplies from them you can post your plans for repair and they'll give you layup schedules.. the owner is an honest to gosh marine architect, so he knows what's right to use.

You can only use biax without mat if you're using epoxy, but if you do, it's easier to make 17 oz biax form corners than 12 oz with mat....

Erik

 

[86RajunCajun]

Re: 1208 biax pros n cons..

Awsome info guys, thanks a lot!

I do totally want a strong boat, but also a very light and nimble boat. It is a 17 ft bass boat with 150 horse, i like speed and ease of use.

I will be shopping around soon for glass supplies and i will take a look at the sources you listed. Thanks for those!

The center console/helm i am aiming to get will be pretty unique to my boat but the basic design idea comes from the allison bass boats center helm design with rear bench seating. Ill get some pics of my plan soon. I have been so darn busy working i rarely get time to get in the shop or even on the net!

Thanks again for the info, very helpful!

RC

 

[NSBCraig]

Re: 1208 biax pros n cons..

Wow slow up then...

6 layers on your transom is way overkill..tab it and cover it withone layer you only need to attach it and seal/ protect it.

Same with your knees the wood is strong enough to gusset the transom all you need to do is seal them and protect them from damage that will ruin your seal and then in turn rot the wood.

And your helm just seal it up with some biax or a layer of csm and some cloth.

Looking forward to see your pics.

(I know it's easy to think overkill, I'm still struggling with ti myself)

 

[erikgreen]

Re: 1208 biax pros n cons..

Wow slow up then...

6 layers on your transom is way overkill..tab it and cover it withone layer you only need to attach it and seal/ protect it.

Same with your knees the wood is strong enough to gusset the transom all you need to do is seal them and protect them from damage that will ruin your seal and then in turn rot the wood.

Um... no.

There are exceptions to every rule, but the transom is one area where you MUST have thick enough glass to take a lot of force. One layer won't do it, period.

The transom's job is to transfer all the force of driving the boat forward, turning etc to the rest of the hull, usually through the stringers. It's rigid and made from thick wood so it can do this. Because it's so thick, usually you don't need to reinforce it with glass... it's not necessary for most boats to make it a composite panel, it's strong enough on its own. But even for those boats you MUST make sure it's strongly attached to the rest of the hull. Ideally 2-3 layers of 12 oz or better glass tabbing over properly applied putty fillets at the edges.

One layer of glass to cover it (seal the transom wood and protect it) is fine, and you can use more if you want extra security/strength. It's probably not NEEDED, but it will add lots of strength, which isn't a bad thing, and two layers of 12-17 oz cloth don't add much weight.

The stringers are the next critical component in the boat. Unless the knees they attach to the transom with are huge (as in the full height of the transom), you need to ensure they're tabbed with the same layup as the transom edges are. The transom sends force to the hull via the stringers, and the hull sends force to the transom via the stringers. If that joint breaks for any reason you're in a lot of trouble.

Sure, no need to go nuts and put on five layers of 32 oz fabric. Just like there's no need to make your deck out of 3/4" ply covered with 12 oz cloth. But the transom/hull joint and the transom/stringer joints are the one area where overkill is definitely a good thing.

Not having glass reinforcement worked in the old wood boats... but if you look at one of them, I think you'll find they used a huge amount of solid hardwood in those places for the same reasons.

Erik

 

[NSBCraig]

Re: 1208 biax pros n cons..

No way man.

Your bolted to that peice of wood in four spots plus your transom eyes plus the all important bonding to the outerskin, gap filling and tabbing.

No way you need to add layer after layer of cloth and mat soaked in resin.

Waste of money and adding weight for no reason at all.

If you want to spend / add more make some knees to spread the stress to the stringers more and buy some transom backing plates from Bob's Machine.

 

[jcsercsa]

Re: 1208 biax pros n cons..

Um... no.

There are exceptions to every rule, but the transom is one area where you MUST have thick enough glass to take a lot of force. One layer won't do it, period.

The transom's job is to transfer all the force of driving the boat forward, turning etc to the rest of the hull, usually through the stringers. It's rigid and made from thick wood so it can do this. Because it's so thick, usually you don't need to reinforce it with glass... it's not necessary for most boats to make it a composite panel, it's strong enough on its own. But even for those boats you MUST make sure it's strongly attached to the rest of the hull. Ideally 2-3 layers of 12 oz or better glass tabbing over properly applied putty fillets at the edges.

One layer of glass to cover it (seal the transom wood and protect it) is fine, and you can use more if you want extra security/strength. It's probably not NEEDED, but it will add lots of strength, which isn't a bad thing, and two layers of 12-17 oz cloth don't add much weight.

The stringers are the next critical component in the boat. Unless the knees they attach to the transom with are huge (as in the full height of the transom), you need to ensure they're tabbed with the same layup as the transom edges are. The transom sends force to the hull via the stringers, and the hull sends force to the transom via the stringers. If that joint breaks for any reason you're in a lot of trouble.

Sure, no need to go nuts and put on five layers of 32 oz fabric. Just like there's no need to make your deck out of 3/4" ply covered with 12 oz cloth. But the transom/hull joint and the transom/stringer joints are the one area where overkill is definitely a good thing.

Not having glass reinforcement worked in the old wood boats... but if you look at one of them, I think you'll find they used a huge amount of solid hardwood in those places for the same reasons.

Erik

Sorry Craig but I have to agree with Erik here !!! there is so much force a outboard puts on the transom, pushing and pulling , one layer I wouldn't feel safe !! I run mine petty hard jumping wakes and all and one layer wouldn't do it , If I remember right I got 3 lays of eglass 28 oz total, using epoxy !! and thats not counting all the tabbing i did !! John

 

[erikgreen]

Re: 1208 biax pros n cons..

Cajun -

We can go back and forth all day about what reinforcement is needed for your boat, but the only person really qualified to tell you is a naval architect who has developed a mathematical model of your hull. I think my suggestions should be pretty close to what's needed, but others may disagree

The only way to get the minimum weight and minimum strength at the same time is to talk to said architect, which I encourage you to do if it really matters to you. But otherwise I'd say be conservative.

Erik

 

[NSBCraig]

Re: 1208 biax pros n cons..

Think about it ply is the core attached to the hull, how many times you cover the ply does nothing to make the transom stronger.

Tin boats with a 150 on it doesn't have layers of glass piled up on the inside of the transom.

Unless your transom is shot covering the inside over and over is only making a thicker protective layer.

It does nothing to help connect that core with the hull.

 

[ondarvr]

Re: 1208 biax pros n cons..

It all depends on the original design, so each of you can be correct.

Using a core can make a laminate much stiffer without adding a great deal of weight when compared to just using more glass and resin to achieve the same thickness and/or stiffness and depending on the final use of the structure the core may need to have different properties.

A transom should be fairly stiff, so adding a core helps and if it didn't have large bolts going through it to hold a heavy engine, it wouldn't need a core like plywood that has very good compressive strength.

Plywood is much stronger than most cores and sometimes it's strength is calculated and used in the design, and other times the load is designed to be carried by the laminate alone and the Ply strength isn't figured in. Then, on many, if not most, of the older designs, there was no engineering done at all, just some guy in the shop said this amount of ply and glass should work. If it failed they added more of one or the other, it may not have been the correct way to do it, but it worked in the end.

The skin on each side of a core should be equal in most applications, this yields the best strength to weight ratio for a flat panel, but there are so many different transom designs with knees, splash wells, contours, heights, widths, curves, etc, that in some applications the ply may be used to mainly build up thickness and not so much for the strength.

Most transoms in small boats are much stronger than they need to be, just look at how many have wood that is no more than pulp, yet get used for many years like that. It?s the same with stringers.

On a flat transom, like most older boats use, having an equal layup on each side of the plywood would typically be the best design, but sometimes all there is is one layer of CSM, or maybe even just some paint on the inside.

I tell people if they?re going to use the same HP motor as it had before, then just replace what was there (if its original) because it lasted thirty or more years and did fine. But if they plan on doubling or tripling the HP (not recommended) like some people on other sites do, then build it as strong as you can.

 

[jcsercsa]

Re: 1208 biax pros n cons..

Thanks ondarvr As allways , You The MAN !!!! I did over kill mine !! I got 4 lay ups on mine and I did use eglass on it all , plus the epoxy !! I just know with that 125 on the back of mine and doing 43 [ I will get 50 out of her ] I wanred to feel safe , And I sure do !! and now that you mention it she is about as thick as the outer skin !!!

So its up to you 86RajunCajun,but two lay up should do great with the 1708 !! john

 

[erikgreen]

Re: 1208 biax pros n cons..

Nice answer, Ondarvr.

The problem with discussions of boat structure is that so much depends on the original design. Like you say, there may not have been much engineering involved.

But guys like me giving advice based on modern composites design can be just as wrong as the older guys giving advice on "what's obviously right" or "the way they've always done it".

Bottom line is, I think, be conservative unless you know what you're doing, and duplicating the original material specs is usually safe, as you say.

Erik

 

[system-f]

Re: 1208 biax pros n cons..

So...anyone try that 1208? I really wonder if it is that much easier to work with than 1708.

 

[erikgreen]

Re: 1208 biax pros n cons..

I've used it occasionally... it is a lot easier to make conform than 1708. Of course, 12 oz biax without the mat is easier still, except you have to be careful around corners to make sure the fibers run the right way.

Mat is still the most conformable stuff, and you don't need strength if you're just coating something with glass to waterproof it.

Erik

 

[system-f]

Re: 1208 biax pros n cons..

Mat is still the most conformable stuff, and you don't need strength if you're just coating something with glass to waterproof it.

I have a heck of a time getting 1 1/2 oz csm to go cap my stringers, but that could just be because the csm is too thick.

 

[ondarvr]

Re: 1208 biax pros n cons..

So...anyone try that 1208? I really wonder if it is that much easier to work with than 1708.

Typically yes, but cost wise it will normally be more expensive for the same strength.

Both use the same amount of mat, so to duplicate the strength of the 1708 there will be more mat used...this equals more resin also...which means more weight and higher cost for the same strength.

Plus 1208 requires the same processing time to be made as 1708 and less is sold, so the cost per pound can be higher, sometimes much higher and this can also make it harder to find.

The next factor can vary from brand to brand, or even batch to batch. Depending on how its made and treated, even some of the lighter fabrics can become stiff and difficult to work with, others are limp even in the higher weights.