Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-05-2006, 08:35   #1
Registered User
 
markpj23's Avatar

Join Date: Nov 2005
Location: Black Hills, SD
Boat: Now Boatless
Posts: 1,148
Images: 47
Depth Sounder Thru-Hull Alternative?

I have a Datamarine unit where you remove the 2" through-hull plug and insert the depth sounder head just prior to getting underway. I always approach this task with sweaty palms and elevated heart rate... and on my best day I still manage to get salt water everywhere. The whole thing just gives me the heebie-jeebies....

I recall an alternative where a water-filled cofferdam of sorts is built against the hull and the transducer is fitted into it. So the depth sounder head / xmitter is not exposed to external sea water but rather sits in a water or silicon-liquid filled box. Somehow the instrument compensates for the different density of the hull vs water and calculates the true depth. I'm sure that steel or aluminum hulls would radiate a true sound wave, but am not so certain that fiberglass, due to its layered construction, would be able to do so.

I guess my options are:
1) live with the mess and get over my anxiety
2) send the mate to the bow with a lead line (not likely she says)
3) install a diving alarm

Can anyone here recommend an alternative system?
__________________

__________________
Mark
markpj23 is offline   Reply With Quote
Old 15-05-2006, 09:15   #2
Registered User
 
CaptainK's Avatar

Join Date: Sep 2005
Location: Phoenix, Arizona... USA
Posts: 2,386
Images: 7
Mark.

The version I seen was instead of silicon in the box. I seen mineral oil placed inside the box.

Then the transducer is placed inisde the box. The wires run through the back of the box to the interior of the bottom of the boat.


__________________

__________________
CaptainK
BMYC

"Those who desire to give up Freedom in order to gain security, will not have, nor do they deserve, either one." - Benjamin Franklin
CaptainK is offline   Reply With Quote
Old 15-05-2006, 09:18   #3
Registered User
 
jemsea's Avatar

Join Date: Feb 2005
Location: Cruising The US East Coast
Boat: Sceptre 41
Posts: 160
Images: 4
Hi Mark,

On a Cal 22 that I knew I was going to sell soon and didn't want to put in a thru-hull I mounted a Hummingbird fish finder to the inside of the hull using Lifecaulk. I was careful to have no air bubbles between the sender and the hull.

It worked great. I was never in water over 60 feet deep using the boat on lakes but it found fish at that depth plus gave bottom contours.

From my experience as long as your hull is solid fibreglass with no air pockets it will work.

I've also heard of, but not tried, mounting a piece of pvc pipe of the correct size to the hull, then partial filling with non freezing liquid in which the sender is submerged and then sealing the pipe over the top of it.

I know this is not exactly what you are asking about because you already have a hole in the hull but hope it helps you find a solution.

John
__________________
jemsea is offline   Reply With Quote
Old 15-05-2006, 09:42   #4
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Why do you ”... you remove the 2" through-hull plug and insert the depth sounder head just prior to getting underway ...” instead of just leaving the transducer (more or less) permanently installed?
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 15-05-2006, 13:46   #5
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
Gord is spot on. You don't need to remove the Transducer. It is designed to permananetly stay in place. The only unit that normally comes out is the paddle wheel transducer.
However.
There are two ways to do a "none through hull" fitting. Both require the face of the Transducer to be in contact with the hull. The easiest is to simply glue the unit to the hull using epoxy. You have to ensure a good clean hull surface. This technique means the transducer is there for keeps.
The second is to use a box filled with a mineral oil. This essentially does exactly the same as the epoxy glue, but allows removal if needed. The oil ensures no air bubble between the transducer face and the hull.
Both techniques equate to reduced performance, than if the unit was attached through hull.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 15-05-2006, 13:52   #6
Registered User
 
markpj23's Avatar

Join Date: Nov 2005
Location: Black Hills, SD
Boat: Now Boatless
Posts: 1,148
Images: 47
This is a paddle-wheel type transducer and leaving it in all the time would foul it with marine growth. I've also seen and been told that painting these with anti-fouling paint can lead to problems, but perhaps that is the answer? Not sure how I'd keep the paddle wheel mechanism free of growth however....
__________________
Mark
markpj23 is offline   Reply With Quote
Old 15-05-2006, 16:49   #7
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,055
Mark, there is no way to mount a paddle-wheel inside the hull. Paddle wheels are speed sensors, not depth sensors. (I suppose you could have a combined unit?) And you are right, a paddle wheel in most waters should be pulled every time you leave the boat or it will become packed with critters. You *can* paint many of them with bottom paint, or the evil but effective tin-based bottom paint (sold in spray cans for use on aluminum outdrives) and that might even let you leave it in the water.

As long as the paint doesn't make the wheel bind (and doesn't cover a depth sounder if there IS a combined transducer in there) you shouldn't have a problem. I know some yards that get happy with the paint and jam up the paddle wheel, but a few minutes with a knife and toothbrush solve that.

But there really should be no reason to fear sinking the boat. If you get practiced at "pull with this hand, plug with that hand" you shouldn't take more than a pint to a quart of water in that gushing moment.

Its like the first time a boat is heeled hard over--you may get anxious but after a while you get used to it and accept it as normal.
__________________
hellosailor is offline   Reply With Quote
Old 15-05-2006, 17:43   #8
Senior Cruiser
 
Starbuck's Avatar

Cruisers Forum Supporter

Join Date: May 2005
Location: Long Beach, CA
Posts: 827
"The Boat is Sink— oh, okay, the plug is in. Whew!"

Yeah, Mark, this is the speed log. The switch becomes reasonably mundane with time.

I remember the first boat I owned that had one of these. I was pretty panicy when I saw that two inch flood of water coming into the boat.

And when I think about pulling the plug out and letting my current boat play submarine ("Dive, Dive!") momentarily, yes, it still gives me pause. But it's only a couple of seconds, and I'm sure you have the sender/plug ready to go each time. So even if you fumble it and it takes a whopping five seconds, you can't let a whole gallon into the bilge. As has been said, on a good day, it's under a pint

I do wish there were a completely dry way to do it: partial pull, close a valve, pull it out completely, take your time with the plug, slide it in partially, open the valve, and finish the insertion. But people would probably get lazy and depend on the valve instead of the plug.

I usually leave the sender in for a couple of weeks at a time, and switch it for the plug momentarily to clean, spin the paddle, and replace, or when I know I'm not going to be around the boat for a while. Reduces the number of times the exchange has to be done, and this is never a problem for me.

Confidence will grow with experience.
__________________
s/y Elizabeth— Catalina 34 MkII
"Man must have just enough faith in himself to have adventures, and just enough doubt of himself to enjoy them." — G. K. Chesterfield
Starbuck is offline   Reply With Quote
Old 15-05-2006, 20:54   #9
Registered User
 
BC Mike's Avatar

Join Date: Jun 2003
Location: Gabriola BC
Boat: Viking 33 Tanzer 8.5m Tanzer 22
Posts: 1,034
Images: 5
Transducer

If it is a depth sounder then epoxy the transducer to the inside of the hull, if the hull is solid. You can do a test using silicone, stick it on and try it in deep water. If the readings are okay then stick it more peranently in place. If it is a paddle wheel for a knot meter, the new Raymarine units have a couple of flaps in the tube that slow down the water intake, but your hand over the hole also works until you are ready with the plug, or paddle wheel. The new Raymarine unit also advices to use antifouling paint on the paddle wheel and through hull fitting.
Michael
__________________
BC Mike is offline   Reply With Quote
Old 15-05-2006, 23:06   #10
Registered User

Join Date: May 2005
Location: Pennsylvania
Boat: Tayana 37, M-20/I-20 Scow
Posts: 250
Mark
Consider the next time when you remove the paddle wheel to apply a heavy dose of medicated baby diaper cream to the wheel and its support structure ... but not on the spindle area - apply thick and let dry. Desitin® is the USA brand that I use to good effect. The antibiotic in the 'waterproof' cream will help keep the growth to a minimum.

If you apply thin bottom paint consider to use oxytetracycline (from a veterinarian). Just pulverize the tablets to a very fine powder and mix it into the bottom paint ... apply the paint thinly. Oxytetracycline is an antibiotic will also keep the growth to a minimum.
__________________
Richhh is offline   Reply With Quote
Old 15-05-2006, 23:08   #11
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
I haven't seen a trough hull sounder trany with a paddle wheel as well. But OK. I keep my paddle wheel in the hull permanent. I can pull it, but I decided to try and see how long it would work. I coated a liberal coating of Lanocote over the thing and it works fine. It has been in the hull for 1yr now and I still have it work every time I go out. I don't get a lot of weed growth where I am, but even if it meant having to pull and recoat with lanocote every 4 or 5 months, It has to be better than what you are doing now. My through hull is 4-5ft below the water line, so when I pulled it for the first time, the blast of water that hit me in the face, fair soaked me, the inside of the boat and I got such a shock, I struggled to get the bung back in the hole. I don't intend doing that to often.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 16-05-2006, 09:28   #12
Registered User
 
markpj23's Avatar

Join Date: Nov 2005
Location: Black Hills, SD
Boat: Now Boatless
Posts: 1,148
Images: 47
Thanks guys... so I can use some tricks to keep the growth off of the paddle wheel OR I can suck it up and sound the diving alarm...

Anyone know how to calculate how much water can move through a 2 inch pipe in 2 seconds? Hull depth at the through-hull is 3 feet. So the equation would probably be:

2" x 3ft x I-factor (how impaired I am from the grog) = Holy @$##$%!!

Seriously - anyone know how to calculate that? How about it Gord? I know it has to be much more than a pint or two.... plus that salt water gets to wash over my iron mast step on its way overboard... not pretty.
__________________
Mark
markpj23 is offline   Reply With Quote
Old 16-05-2006, 11:10   #13
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,055
Mark, don't even try to do the numbers. No matter what they are, it can't sink the boat!<G>

I don't like the idea of throwing antibiotics in the water. That breeds antibiotic resistant critters "in the wild" and that means the next time you cut yourself, there's a better chance you'll be infected by something that antibiotics no longer kill. A very, very, bad practice.
__________________
hellosailor is offline   Reply With Quote
Old 16-05-2006, 11:39   #14
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Approximate Flooding Rates, for smooth holes at selected depths, are calculated using the formula:
Flooding Rate in gpm = 20 x d x square-root of h
where:
d = diameter of hole in inches
h = depth of hole underwater in feet (head)

Hence, for a 2" dia hole at 3 Ft depth:
Q = 20 x 2" x root 3 = 20 x 2 x 1.73 = 69.2 gpm (4,152 Gal per Hour)
then
69.2 / 60 = 1.15 gal per second, or 2.3 gal in two seconds

The actual flow rate ('Q') will be less than calculated above, due to frictional & turbulance losses at the aperture.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 16-05-2006, 11:54   #15
cruiser

Join Date: Nov 2004
Posts: 4,525
I do the same as Wheels. I remove the knot log (paddle wheel) once a season. I also coat it with bottom paint very carefully, with a Q-tip. You can load it right up with paint, but watch out to be sure the paint doesn't create any surface on the wheel which can drag on the housing for the knot log.

I get at least a season out of a knot log this way. If it ever does stop working you can always pull it out like you are doing now. But why do it so many times when you don't need to? Just becomes a nuisance.
__________________

__________________
ssullivan is offline   Reply With Quote
Reply

Tags
depth sounder, thru hull

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Opinions on Cruising Sailboat? leesureman Monohull Sailboats 32 05-07-2009 19:23
Voluptuous lady gatecrasher xinxinxinaa Meets & Greets 33 08-07-2007 16:18
Hull polishing irwinsailor Construction, Maintenance & Refit 22 13-01-2007 21:15
A Primer on Fiberglass Construction Jeff H Construction, Maintenance & Refit 25 17-11-2005 11:21
Depth Sounder Troubleshooting exposure Construction, Maintenance & Refit 9 10-02-2004 15:47



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:27.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.