Osmosis Moisture Meter

[Wandering Star]

Thinking of DIY treatment of an osmosis riddled hull. The surveyor mentioned he used a Tramex Skipper meter to measure the moisture content of the hull and the readings were “off the scale”. I know of another meter a Sovereign make which is used by surveyors too. as the hull dries out, I’d like to take regular hull moisture readings myself to monitor the drop until it stops dropping at which point I understand it won’t drop further and I can consider the hull is as dry as it ever will be.

But, the Tramex Skipper costs a whopping £370 or so and I wondered if there were other meters I could use. I see Chinese meters for measuring the moisture in wood or concrete costing £20 or so, would they do the job? I’m not looking for accuate readings, I’m only interested in watching a drop in relative readings taken over several days. Anyone able to give advice?

 

[jwilson]

Most of the cheap meters rely on prongs to stick into wood or concrete: you can't really do that on GRP. Go a bit more expensive though and you can get 'pinless' ones: they ought to work, but it would be good to compare readings with a Tramex or Sovereign to get an idea of what is a "good" reading.

 

[johnlilley]

I use a Tramex Skipper and occasionally a Sovereign in surveys. As a back up I also purchased a cheap Chinese wood moisture meter on Ebay to see what it was like.
Less than £20 this particular one works using the pad on the back face similar to the Tramex. No pins. It also has about 10 different scales and the default start setting is 3. I have used this frequently now and compared it with Tramex range 2 (the most sensitive range for Grp). The digital display reads fro 0 _100 and compares precisely with the readings obtained on the 10_20 scale on the Tramex. In other words when the Tramex reads15 on the 10_20 scale the other meter reads 15 and corrolates almost precisely throughout the Tramex Ranges with a bit of practice. . It seems very precise and easy to use subject to the understanding of the normal variance of readings. If nothing else it can give very accurate comparison readings and if one had temporary access to Tramex Skipper readings of the same area to ensure similar readings, would make a very reasonable ansd inexpensive tool for an owner

 

[Wandering Star]

Hi John,

That sounds promising and th sort of experience I needed. Could you tell me what make & model you purchased? Otherwise, could you describe exactly what attributes I need to be looking for?

Thanks to JWilson too.

 

[longjohnsilver]

I have a Tramex that I have lent out to other forum members. If there’s any way you can pick it up from near Exeter, and return it the same way, you’re welcome to borrow it.
Unfortunately I’m not happy with posting it.

 

[Graham_Wright]

I bought one of these;-
Extech Pinless Moisture Meter | eBay

It has two settings - wood and "other building materials".
However, a trip round the hard standing shows that there is a variation between boats and I know mine is wet. Interestingly, wood which appears to be vey dry gives a maximum reading on both settings. It also confirms that the human body is 99% water!

It would be interesting to compare with a Tramex.

 

[johnlilley]

DAMP METER DIGITAL LCD MOISTURE DETECTOR WOOD HUMIDITY TESTER TOOL HOME | eBay
seems very similar to the one I described. Obviously I cannot endorse this particular seller or item but it is identical so far as I can see. Seems to be very few pinless meters available now other than this one. Might find it elsewhere if you look hard

Hi John,

That sounds promising and th sort of experience I needed. Could you tell me what make & model you purchased? Otherwise, could you describe exactly what attributes I need to be looking for?

Thanks to JWilson too.

 

[Wandering Star]

I have a Tramex that I have lent out to other forum members. If there’s any way you can pick it up from near Exeter, and return it the same way, you’re welcome to borrow it.
Unfortunately I’m not happy with posting it.

Hi LJS, thanks very much for the generous offer, unfortunately I’ll have to decline as I don’t t down your way except when I’m sailing, also I’d be mortified if I damaged someone else’s property. I think I’ll go with one of the Chinese jobbies off eBay, if you‘ve finished using and wanted to sell your Tramex, I’d be very pleased to buy it off you for a fair price?

 

[Wandering Star]

DAMP METER DIGITAL LCD MOISTURE DETECTOR WOOD HUMIDITY TESTER TOOL HOME | eBay
seems very similar to the one I described. Obviously I cannot endorse this particular seller or item but it is identical so far as I can see. Seems to be very few pinless meters available now other than this one. Might find it elsewhere if you look hard

Thanks for this John.

 

[superheat6k]

Flow chart for assessing Osmosis in boats ...

Has it sunk ?

No - buy the boat

Yes - don't buy the boat

 

[Tiderace]

I'd suggest if you are worried about spending £370 for some kit, the boat isnt for you as that will undoubtedly look like chump change by the time you are done!

 

[Wandering Star]

I'd suggest if you are worried about spending £370 for some kit, the boat isnt for you as that will undoubtedly look like chump change by the time you are done!

Never having been wealthy, I’ve still managed to sail far & wide by looking for cheaper solutions and DIY solutions, it’s how I manage to afford it. £370 certainly isn’t chump change to me for an item I’ll probably never need to use again and it does pay for the cost of a years insurance or secondhand inflatable.

 

[longjohnsilver]

I'd suggest if you are worried about spending £370 for some kit, the boat isnt for you as that will undoubtedly look like chump change by the time you are done!

That’s unfair. It’s for a piece of kit the OP is only ever likely to use once. Not for something that will be used every time he uses the boat.

 

[thinwater]

• Get a cheap meter. Or a good meter.
• Get a chunk (100-200 mm square is good) of FRP similar to your lay-up. Dry it in an oven at 150F (warming setting) for 4 hours and weight it on a kichen scale (nearest gram).
• Read it with the meter.
• Soak in it water for a few weeks. Weight it and calculate % water. Read it. Maybe soak it even longer an re-read for another data point.

Now you have your calibration. I did this with a cheap meter and it did very well.

You really need to do this with ANY meter if you want the readings to mean anything.

 

[Tomahawk]

The first thing to understand is that a moisture meter is not a moisture meter.
It is an induced electrical conductivity meter.

The so called moisture content is actually implied from conductivity of the material being tested. The pratical upshot of which means you need to compare the test area with a known dry area. Even areas that have never been in water will have a residual amount of moisture.

So a cheap meter as above will do the job quite well .. Log the readings at both the test site and the control site and monitor how the hull dries out.

The advantage of the professinal meter is that it can be tuned to measure at different depths of the laminate.

 

[Tiderace]

Never having been wealthy, I’ve still managed to sail far & wide by looking for cheaper solutions and DIY solutions, it’s how I manage to afford it. £370 certainly isn’t chump change to me for an item I’ll probably never need to use again and it does pay for the cost of a years insurance or secondhand inflatable.

That’s unfair. It’s for a piece of kit the OP is only ever likely to use once. Not for something that will be used every time he uses the boat.

My apologies if my response came across as rude, it was not intended to.

What I meant was that the cost of repairing osmosis on a boat will be expensive whatever route you choose; obviously cheaper doing it yourself and as such the cost of the meter will likely appear cheap, even at £370. Although I fully appreciate the intent of ensuring one gets the most cost effective solution at every turn as we all know boats aren't cheap!

You could also consider thermographic survey. Moisture readers only give the reading at the point on the hull, where as thermographic survey will show the entire hull. I use to have a picture of a 50 odd footer that had osmosis, looked like chicken pox; very clever stuff and not expensive per say!

Good luck, and it will be interesting to hear how the project progresses.

 

[Graham_Wright]

• Get a cheap meter. Or a good meter.
• Get a chunk (100-200 mm square is good) of FRP similar to your lay-up. Dry it in an oven at 150F (warming setting) for 4 hours and weight it on a kichen scale (nearest gram).
• Read it with the meter.
• Soak in it water for a few weeks. Weight it and calculate % water. Read it. Maybe soak it even longer an re-read for another data point.

Now you have your calibration. I did this with a cheap meter and it did very well.

You really need to do this with ANY meter if you want the readings to mean anything.

That's a very obvious thing to do (but only when someone else has suggested it!).

I will do that. I think I have some bits that were cut out for hatches and the like.

 

[johnlilley]

Perhaps the quickest way to set a datum on a particular hull (single skin) is to use a starting point of the topsides well above the waterline . Make sure there are no wet linings, condensation inside or out or timber encapsulations at that point, but simply doing a number of readings on the topsides will get a working average with a sensitive meter then compare that with the underwater hull readings. There almost certainly will be a considerable difference, if not that suggests the meter is not sensitive enough.

 

[thinwater]

Perhaps the quickest way to set a datum on a particular hull (single skin) is to use a starting point of the topsides well above the waterline . Make sure there are no wet linings, condensation inside or out or timber encapsulations at that point, but simply doing a number of readings on the topsides will get a working average with a sensitive meter then compare that with the underwater hull readings. There almost certainly will be a considerable difference, if not that suggests the meter is not sensitive enough.

^^ This too. There are nearly always some area you are sure are dry. Do remember that cored areas and solid areas are very different, and thickness also matters. As Tomahawk wrote, it does not measure moisture directly.

 

[James W]

“Off the scale” from the surveyor is not overly helpful. If he’d given you numbers and written them on the corresponding areas of the hull, that would have at least given you a starting point. The Tramex is very good at finding moisture, be sure to think about where your heads, water tanks, stringers are make sure the bilges are dry before taking readings.