make of boat and testing balsa core

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I have recently purchased what I believe to be either a Microplus of some description of a shetland. I'm not sure as although the top deck appears very like to images available on microplus.dk and the shetland owners association, the hull is different.

The closest match I can find to the hull is this image http://www.microplus.dk/small34600154_0.jpg but I cant find this in the models section...

I can take pictures in the next few weeks that may help...


My main question though is this:

I am told the microplus was constructed with a balsa core layed into the laminate of the cockpit floor, I have always had concerns over the core becoming damaged/water logged/rotten. What are my options in determining:

1. Is the boat is of balsa core construction? Options I see are, drill a sample core through the hull? size of core? how is the resultant hole resealed?

2. Assuming the boat is balsa cored, testing the integrity of the core. Can damaged sections be felt through the outer grp by applying pressure? I can potentially use ultra sonic thickness checking gear if it would help.

Any help that could be provided would be gratefully received...

Many thanks in advance,

Kev
 
Kev
I don't know the model boat but probably 95% of the fiberglass boats of the last few decades have balsa in the deck and cockpit sole. Did you have it surveyed? A surveyor's report would show and indications of moisture.
There are several methods of checking for moisture in balsa. The simplest is to take a small phenolic (not metal) hammer and tap, listening for dull sounding sections. The other way is to use a moisture meter. Moisture meters are fairly expensive and will not give a yes or no answer. They have to be calibrated first with a known dry substance - usually a piece of glass. There are many things that can trip up a moisture meter. Matal either in the layup or directly under will read as wey when it's not. If coremat is used in the layup against the gelcoat as it sometimes is the area will read as dry when it may not be. In extremely cold weather they cannot be used effectively. Condensation on the surface will also give false readings. If you notice flexing of the top skin it doesn't always mean moisture but does mean delamination of the top layer.
I would never drill a core sample to check. The best solution is to remove a piece of hardware installed in the middle area of the deck. The deck edges are usually not cored near the hull/deck join. Sometimes if you can get at the inside of the deck from below you are able to see the balsa squares as there is rarely pigment in the resin.
If it is cored the best way to prevent water intrusion is to pot all through deck fittings by removing them and overdrilling the holes, sealing from below, filling with thickened epoxy and then redrilling for the fasteners. This is something all manufacturers should have done during construction but it is rarely seen.
There is nothing wrong with balsa decks as long as fasteners are installed correctly to keep the core dry.

http://www.pbase.com/mainecruising/moisture_meter
http://www.pbase.com/mainecruising/sealing_the_deck
http://www.pbase.com/mainecruising/rebedding_hardware
Here are a few links, one on moisture meters and a couple on sealing fastener holes.
 
Many thanks for your prompt reply, it was the hull I was more concerned over, I will try the tapping with a nylon mallet and see if I can hear any dull areas...

So there is not really any way of testing for the presence of a core?
 
Just to clarify, I may not have described my concerns well. The cockpit floor is wooden I refer to the hull itself as per the below taken from another forum:

"
Here's where the balsa core is.It's laid INTO the hull of the boat-ie fibreglassed in and is part of the hull.It needs the test with the heel of your hand to tell if it's gone soft as you HAVE to be able to compare the feel of it with the feel of the rest of the hull in the cockpit area.
IF you've got the problem (there needs to have been a hole through the inner or outer skin at some point coupled with water getting in there) it will be obvious as there will be a very definite soggy feeling in the area where water has got in compared to the rest of the area.
This is USUALLY local to somewhere the inner skin of the cockpit has been damaged at some time.Drilling a hole and prodding one area through the cockpit floor isn't valid for that reason.
If you can't do the hand pressure test on the inside because of the inner floor, do it from the outside-but you'll need to use a fair bit more pressure with the heel of your hand as the bottom layup is thicker than the inner cockpit skin layup.The balsa core WILL be in your boat-it's the way the 501 was laid up.
any one shed some light on this thanks
"

Again may thanks
 
Kev
What kind of boat is it? There must be some item attached to the hull you're concerned about. This can be removed. Looking at the hole it is installed in will tell you if there is a core or not. Not many hulls are cored but the majority of decks are. The previous post is not correct. The test with your hand has 2 faults. One is the core is not mushy until it rots and if just wet it can be very solid still. The core doesn't rot that quickly. and moisture alone will not always separate the core from the skin along the bond line. Two if the skin is thick enough that method will never work.
 
If there are no penetrations through the balsa core why worry about it. Balsa has been used in many hulls of all sizes and the only issues are where there are holes through it to mount thru hulls, transducers, or drive shafts. If this is not the case it should be fine as there is no way for water to get in without a break in the inner or outer shin. I wouldn't cut a hole in the bottom as you will then have to repair it properly. If the balsa core is wet the boat won't fall apart. It is there as a stiffener for the panels on the bottom that are very probably thick enough by themselves for strength. The balsa with a thin glass layer over it will stop the hull bottom from flexing. Here's a link I'm not sure you're aware of for the Microplus. http://www.microplus.dk/
 
Last edited:
Yes, highly unlikely the hull will be balsa cored. Microplus were cheap and relatively unsophisticated boats and the shape of the hull is sufficient to give the required stiffness with solid layup. You may find re-inforcement stringers in the flat panels aft and the cockpit floor may have balsa to stiffen the large flat panel. The transom may also be sandwich construction depending on the HP rating, but the sandwich filling is likely to be ply.

Hope this helps.
 
Turns out the boat was build by Marina Boats Ltd. Warwickshire.

Anybody know anything about this firm or the boats they produced?

Any info would be great!

regards,

Kev
 
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