Installing a Thru Hull Depth Finder Yikes

[HideAway]

After many failed attempts using an in hull transducer - Compac hulls are too thick - and giving up on the lead line I found a very cheap Horizon depth finder at a marine sale.  I have tested it and it works great thrown over board so now its time to suck it up and drill a hole - ye gads - in HideAways bow.

I thought the convenient flat space under the vee berth in front of the head would be perfect but it seems to be about two inches thick and comes out on the vee of the hull.  The other two 23 Compacs in the club have the transducer installed slightly off center of the hull in front of the keel.  This angles the transducer sideways a bit. 

I see no other solution but I wonder how much the angle affects the accuracy of the device.  Does anybody have experience with this?  Matt

[curtisv]

Matt,

Heel the boat and the transducer is on an angle.  It still works.  It reduces the maximum depth at which it will give a reading.  So if you are in a few 100 feet of water and need the depth for navigation reasons, you'll have to reduce heel for a moment.

I had two thru hulls for the head intake and discharge fore of the keel so I put the transducer on the port side in the flat spot which is under the bunk at the widest part of the hull.  Speed is on the starboard side.  On a port tack I can put her over to the point where add some waves and the transducer is out of the water.  Get some wild reading then.  Otherwise its fine on anything short of rail in the water heel.  Where fine means it reads OK down to almost 100 feet when heeled way over.  It reads down a lot further if the boat is upright.

If you have the room to put it forward of the keel that is a fine place for it.  Its nice to know the depth in front of your keel even if it only gives you an extra few seconds at very slow speed.  At that point in all but the cloudiest water you can just look at the bottom.

Curtis

[Bob23]

   When I bought Koinonia, she already had one installed to the starboard side of the aft section of the keel. The hull is about 3/8 inch thick back there and kind of flat so there is no angle issue.
   Matt: Thanks for the heads up about hull thickness and it's affect on non through hull transducers. I was gonna remove my thru- hull one and replace it with a bond-to-the-hull one but how thick is too thick? I would much rather know the water depth ahead of me a bit than behind me.
   I would really love to have no thru hull openings in my 23 but alas, such is life.
Bob23

[HideAway]

Curtis,  That flat spot forward of the keel is where I glued the others and would be my first choice for the thru hull but there is no flat spot on the exterior.  The hull begins to curve which would leave a gap.  I suppose I could glass in but I really hesitate to do that.

We have been using a lead line for many years to scope out anchorages but a lead line is difficult to use underway for navigation. 

Bob23 I have heard there are tranducers that can be mounted up to 20 degrees rise glued inside but I have never found one.

What got me thinking about all this was the the test I did in a slip showed the depth at 47 feet - Ha  At most these slips are six feet.  Turned out the transducer was nearly horizontal as it hung over the side.

I m dreading cutting the hole, fortunately I have engine work to do first-  You know those little screws used to drain the gear box on an out board?  They have washers --- don t lose the washers  if you fail to put them back water gets into the oil.  And if you fail to tighten the lid on the can of bad oil you put in your pickup bed then leave it to roll around a week before you in vestige the smell you have a real mess-  Just a rumor you understand - it couldn t have been me that did that--right

[skip1930]

Well ain't no big deal. Two~2 inch dia holes drilled through the hull six inches in front of the keel on my CP-19, and six inches to either side of the centerline of the boat positions my Raymarine ST-40 Bi-Data unit. One instrument is for sounding depth and the other is a paddle wheel [you can pop it out from inside the boat while still in the water to remove Zebra muscles if the paddle stops turning.] Here are the pictures. Ohh a 16" x 16" hatch behind the compression post sure makes the job easier. You'll have to remove a little sound deadening foam to find a clean bottom to place the instruments. I rented a hole saw from Ace and had it back within 1/2 hour...no rental charge. Cool!
Paddle wheel on the port side. Depth on the starboard side. Try not to purchase a depth sounder that is a big huge blob hanging down from the hull. Who needs more drag through the water? Just goop both instruments up with 3M-5200 slow set and screw down the nut a little more then finger tight. Not a drop will leak into the hull.
The plug from the hull I used as a washer to hold the pin in my trailer extension slider tube up just a little bit...the pin seams to bind if it's allowed to fall all the way down. That brown ring holding the pin up is the 2 inch plug from the bottom of the boat. I never cleaned the Marine-Tex off the bottom of the keel after gluing on my saw cut 6mm marine aluminum KEEL BOOT. Shame on me. But can't see it when it's in the water. LOL.

skip.

[Bob23]

   I know about those rumors, Matt. I'm sure you are not speaking from experience. It is also rumored that after changing the oil in one Toyota truck, failure to replace the filler cap makes a terrible oily mess under the hood which creeps up the winshield as one drives. It's just a rumor also.
  I didn't like cutting the hole in the bottom of Koinonia, either. But she still floats so I must've done something right, right? Be sure to coat the exposed fiberglass with epoxy to seal it up. But you already knew that.
Bob23

[brackish]

Mine were already installed when I bought the boat.  The depth is on the starboard side it is off then centerline on the starboard side, as I recall, maybe slightly forward of the keel. The speed log is on the port side, just forward (internally) of the mast support bulkhead, with access in the first V-berth locker forward of the bulkhead.  It seems the depth is fairly accurate, although my only verification is leaving it on and jumping off the boat for an approximate measure in shallow water.  The speed log does not seem to be accurate, shows a wide disparity between a port and starboard tack when close hauled. 

Know what you mean about hating to drill those holes.  I've had an installed auto bilge pump in since last fall, just haven't drilled the hole for the discharge line.   Have never had a drop of water in the bilge to date, but you never know...

[curtisv]

Curtis,  That flat spot forward of the keel is where I glued the others and would be my first choice for the thru hull but there is no flat spot on the exterior.  The hull begins to curve which would leave a gap.  I suppose I could glass in but I really hesitate to do that.

What I meant was the flat spot on the exterior just off to either side.  Just forward of the keel is flat but this is where it is very thick and the interior above it is unusable - under the head if I remember.  I have the head intake and discharge where Skip shows his transducers in his photos.  If I were smart I would have just widenned one of the existing holes for the depth transducer and put one of the head hoses further back.

Most of the shoals in Nantucket Sound that I pass over are 15-20 feet (coming up from depths over 100).  Those don't even matter much for a boat with under 3 foot draft since it just means choppy waves when conditions are rough.  The few 6 foot shoals do matter a lot more.  Entering or leaving Nantucket Sound by way of Polluck Rip, the 15 foot shoals do matter when the ocean waves are running high.  That chop can be really nasty but in good visibility you can see the chop on either side of the channel before you head into it.

A look at our local charts shows why a depth sounder is handy to have.




btw- These are old charts and the second is no longer at all accurate.  The point is that there are a lot of 1s and 2s and those are in feet.  The white is deep.  The blue is under 6' depth.  The green is above water at low tide.  Tidal range at that time was 4 feet inside the Bay and 8-9 feet in the ocean.

Here is the outside of Polluck RIp Channel.

I m dreading cutting the hole, [...]

That is definitely the hardest part of this job.  Once you have a two inch hole in the hull there is no turning back.

Here is the hole before putting a transducer in.



And this is the block of wood on the inside.



I used a block of oak and tapered the sides as much as I could with a table saw.  There are a few layers of mat and cloth and then the block and then one layer of mat and cloth over the top.  I used epoxy.  I drilled slightly oversize, epoxied the inside of the hole and redrilled.

Curtis

btw - If you forget to look at your depth gauge this is what can happen.

[Bob23]

We have similiar depth conditions here in The Barnegat Bay in NJ. I once got Koinonia hung up on a submerged former island. They are on the charts but are never uncovered so you can never see 'em. There are a group of 5...I know where 3 are.
Bob23

[cp23enough]

Matt, I feel the same way about cutting holes in the hull. I installed a hawkeye in hull transducer forward of the keel. It is off center but I puddled the epoxy with a little clay dam and aimed the transducer straight down. So far its working fine.

[curtisv]

Bob,

Kinda reminds me of what they say of Don Streets cruising guides.  Don knows where all the rocks and reefs are in the Caribbean because he's sailed there so long that he's personally bounced off most of them.

The big former island in our parts (other side really, Cape Cod Bay side) is Billingsgate Shoal, formerly known as Billingsgate Island.  In Eastham there is a spit with one road and a row of beach houses that are very vulnerable in a storm.  The name of the road is "Harms Way".

I've taken a gander at the section of chart 12318 covering Barnegat Inlet and yes it is an interesting entrance.  I take it that is the preferred way to reach Tices Shoal is Barnegat Inlet.

Curtis

[HideAway]

it looks like the 19 has a flatter bottom than the 23.  There is a noticeable rise on the 23s.  Still the best place to install it though.  I did some reading about sealant and decided on 4200 over 5200.   The 5200 is for things you never have to remove, although there are solvents now from what I read 5200 is very difficult to remove.  The installation instructions advised not to mount the plastic transducer in wood because the wood may swell and crack the plastic.  I have a water tank in front of the head but there is still room for the transducer.

Those charts look a lot like what we have too.   Tampa bay, as large as it is has a depth of only 12 -15 feet so when the wind blows off the gulf it can get nasty quickly as we found out recently.  it was last surveyed in 1856 - a real confidence builder that.  Boats drawing 5 feet spend most of their time in the channel  and sometimes they have to wait for the tide to get into our marina.  A boat drawing 6 foot is a waste of money.

It will be a couple of weeks before I can install the depth finder then I still have the engine issue and a storm damaged Bimini to fix before we launch again.
Linda s sail repairs held up fine on the main so she s on to the jib next.

[breeze]

The thickens of Hull dos not mater
What will disturb the signal is air or a Cord hull
I think the easiest way to address this proplum is to use PVC pipe.
Cut to mach the curve of the hull, don't try to go Thu on the center line of the boat
Seal with 5200 or smilier
The pipe should be vertical and long enough to keep the head from hitting the hull
Mount the transducer in a end center of the cap
drill two small holes in the cap
fill the PVC pipe with water and plug the two holes
this way there is no hole in the boatand the most water that could leek is about a cup

hope this will help
David

[skip1930]

Brackish, you stated, " It seems the depth is fairly accurate, although my only verification is leaving it on and jumping off the boat for an approximate measure in shallow water.  The speed log does not seem to be accurate, shows a wide disparity between a port and starboard tack when close hauled. "

My speed paddle wheel which also drives my distance log appeared to me to be a bit off as well. On a perfect sailing day out in the middle of The Bay of Green Bay where I locked down everything, skinned up to the instrument and let the boat stabilize with my weight moved forward, and just let the boat sail her self at a consistent indicated 4.0 to 4.2 knots I compared my log to that of the GPS chartplotter.  Yep the log was a little slow.

Electronically this deviation can be weeded out according to the owner's manual.
Having done so the GPS and Log reflect similar numbers.  

HideAway; "it looks like the 19 has a flatter bottom than the 23." Yes the CP-19 does have a flatter bottom and she sails fastest when Not heeled over, but rather straight up and down. The CP-19 had a little help from tank testing at a NASA facility. Entirely two different boats from two different designers.

skip.  

[brackish]

Electronically this deviation can be weeded out according to the owner's manual.
Having done so the GPS and Log reflect similar numbers.

That may be so but in my case I have a deviation to GPS reading and then a second deviation port to starboard when close hauled.  For some reason, reads that I'm going much slower on a starboard tack, close hauled.  With everything else being equal, sail position the same, heel the same, telltales indicating the same, no real current or wave action in the lake, I read a full knot slower on starboard, which doesn't show up on GPS.  It's a mystery, but I've chosen to ignore it.  Will inspect the impeller when I pull the boat next month for bottom job and trip to the Gulf.