Forgive me if this is a stupid question but is strength once you get past the fuel tank such a major issue. I understand it is preferable for the hull to be as solid as possible but if filling the boat with some floatation such as foam is going to lead to water absorption and all the repair work that entails is it really necessary to use something which strengthens as well as adds floatation.

And also if the hull isn't stuffed with floatation water will be left standing in the bottom of the boat which you will probably notice and so go looking for the cause?!?! Instead of being soaked up and causing the problems it does.

I know after reading this Im going to stick with the polystyrene I've put in already.

All the best

Brandon.

Hi Brandon

There is no such thing in my mind as a stupid question. Answers may be judged that way!

Consider the strength of your hollow bow section and mine filled with expanding PU foam encased within a wooden bulkhead. (me with no water ingress issues with this boat and the others used over 30 years – and bear in mind that model boats unlike full sized boats don’t stay on the water for that long).

Take your fist or a rubber headed hammer and give a decent clout to your hull.

Yours will probably split and fracture the gel coated fibreglass. My ready to run first gas boat did exactly that when I had my first accident.

My Lynx as shown (earlier on) has subsequently suffered far more knocks than that and its hull has remained pretty much intact without any gel coat fractures. Just a few surface scratches that are easy to fix.

It is of course a matter of personal opinion based upon experience and I accept that opinions vary substantially on this topic.

As I’ve expressed, for my part I like the expanding foam option as it has worked for me giving the necessary bouyancy and strength as an added benefit.


Cheers
Craig

For my part I will use expanding foam in the front 40 percent of my 56 wooden mono.
NOT for the floatation, as this compartment will be totally waterproof as is. The foam will mostly be to strenghten the front part of the boat. Because of this strenghtening, the boat will take much more bashes than if it had no expanding foam.
If the foam is NOT in a COMPLETELY closed compartment it WILL suck in water first time the boat turns over.
These are simple facts given to you from me as a former boat builder.

Cheers!

Woodie.

Marc,
I nearly had the same issue in my 23ft powerboat. Crack in the hull, luckely picked up and the crack didn't go through all the way. Foam filled hulls ride quieter, and I can attest to that, but I also would prefer not to have another again. I like hulls with sealed bouyancy chambers so you can open the drains, and if any water ever comes out you know there is an issue. Have seen a foam filled powerboat dropped 6 levels from a dry stack. Intact, but cracked through everywhere. It would still float although was a write off!

Brandon,
Don't use polystyrene. I believe it doesn't like petrol. Pool noodles are best. Get the Red ones, you boat will go faster.
David

I use the red ones too it works

Kiwiboater,

Ive taken the polystyrene out of the hull and am going to investigate other methods.

I suppose if the compartment with the foam is watertight and you keep an eye on the bottom of the hull for cracks etc there shouldn't be a problem.

Is there a "formula" for putting the foam in the hull or is it just little bits at a time and allow it to expand fully before adding more??

All the best,

Brandon.

Hi Brandon

Personally I totally agree with what you supposed. But I am bound to say that because the foam system has delivered results for me without issues of water ingress or splitting apart hulls etc.

My advice would be to use a two part mix so that you can prior experiment with it and get a feel for how quick it expands and cures without having a can of the stuff that has to be used more quickly.

Importantly prior to filling the void, do ensure that you have several decent sized holes to allow for expansion. If you use it in your current hull I would definitely recommend a bulkhead and do it in at least two stages because the shallow nature of your bow section could lead to pressure inside as the surface area of your exit (vented) bulkhead is relatively small compared to the hull and deck front beyond it.

One way of thinking about it is this:

Fill a long slim rectangular box with this foam with exit (vent) holes at the end, and there is a real risk of blowing the bigger surface area of the tops and sides of the box off.

If the same box had vent holes drilled in the top, the risk would be minimal.

However with a slim mono hull that is not a practical option.

I hope this helps. Others that are fans of this system may add further.

Cheers
Craig

Craig - good points. Your 2 part foam is better, and that is what's used on full size boats. All good points on how to mix and fill voids to ensure that there are expansion holes, large enough, and in the right places.

All,
Re: totally sealed sections.
If say your bow section is totally sealed, and your boat is any sort of colour, see what happens when it's out in the sun. Your 'sealed' chamber will likley start to blow up. My 1st hull has a sealed bow section, and I actually put in pool noodles. The heated up air inside the sealed ara expanded and the deck bowed. Lukily I had a 1/4in drill in my hand so I popped a vent hole through the bulkhead. There was some pressure in there.
Will install a breather/venting system same as what some guys do to their gas tanks. Spoken to other boaters since, and they say, don't do sealed sections.
Leave it open, and lightly glue in or tie in pool noodles. Hollow pool noodles are also useful, for if you have to add weight in the bow, the weights can be put in the so they don.t rattle around.
David

ps Red noodles don't go any faster - just in case anyone actually believes that.
I use blue!

Also remember that the sealed sections on full size boats are usually underneath the floor, under the waterline, whereas in model boats we tend to seal up a bow or sponson section. Exposed to sun/heat.
Full size power boats also have far thicked hulls. They are in most cases white in colour.
David

Hi David

I think you made a very good points about sealed bow sections when the sit in the sun especially when in a heat absorbing dark colour. You only have to leave a plastic fuel container in the sun to see how much it expands with the pressure building inside (albeit gas vapours). The same principle applies with air.

On the pool noodles, until I joined this forum I’d never heard of them let alone found them on sale. My lynx needs buoyancy in the sides towards the rear end to avoid what happened in the opening clip when it was rescued. Having tried pipe lagging foam (not sufficiently buoyant) I managed to find some pool noodles on Amazon and have ordered some to try.

Thanks all of you for your interesting and most helpful contributions on this topic.
Cheers

Craig