I would like to get a fishfinder for speed and depth, but have hesitated because of the need to mount the transducer and paddlewheel. I see that some companies such as Humminbird offer a suction cup mounting kit. So my questions are: Does a transom mount work properly on a sailboat? Would my daggerboard cause turbulence and affect the accuracy? Can it be located so that it still functions when heeling? Do any of you have experience with the suction cup mounting system? If not how have you mounted yours? Some transducers can work through the hull, but to get speed you need a paddlewheel which must be mounted in contact with the water. Thanks for your help Rob Humphreys Oregon City, OR
How to mount a Transducer/Paddlewheel
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Through-Hull
My Raymarine bi-data uses two through hulls located in front of the keel. One is speed (paddlewheel) and the other depth. This is the correct placement on a sailboat. It works while heeling and is not effected by post keel/rudder/prop turbulence. Properly installed, which is not difficult, through hulls do not leak a drop. Mine never have on any boat I have owned.
My Raymarine bi-data uses two through hulls located in front of the keel. One is speed (paddlewheel) and the other depth. This is the correct placement on a sailboat. It works while heeling and is not effected by post keel/rudder/prop turbulence. Properly installed, which is not difficult, through hulls do not leak a drop. Mine never have on any boat I have owned.
I have an old Garmin 185 Sounder/GPS/ Knotmeter,
The sending (tranducer/paddle wheel) unit is mounted on the transom at the botttom edge. It works fine and is very accurate. It includes a fish finder. ;O Trying to find a place to mount the antenna was more of a problem, however, seems to work out where I put it.
The sending (tranducer/paddle wheel) unit is mounted on the transom at the botttom edge. It works fine and is very accurate. It includes a fish finder. ;O Trying to find a place to mount the antenna was more of a problem, however, seems to work out where I put it.
through hull depth transponder
I have the depth transducer "shooting though the hull" and its mounted to the hull in the Laz area - forward near the bulk head and away from the rudder. The hull needs to be solid fiberglass for this to work and it must be on the 26S because this seems to work fine. I initially tested this by using some of the toilet sealing wax (comes in a ring, seals the bottom of the toilet). Just make a good mechanical seal between the transducer and the hull with a glob of wax - work out all the bubbles. This worked but is only temporary as I know from first hand experience that freezing weather will break the wax bond. I ended by epoxying the transducer to the hull surface (JB epoxy - or something which will work on the plastic of the transducer). I have a cheap fish finder however the manual said the tranducer would work fine shooting through the hull. And it does to 100 feet, havent been able to test it past that since that is the deepest water Ive been in. I currently dont have a good reason to watch speed but if occasinally do, I just use a GPS. The PO had a big ol hole in the bottom of the boat for a worn out obsolete speed transducer which I gutted and sealed and I dont like to even think about it (dang, Im thinking about it now..),.
I have the depth transducer "shooting though the hull" and its mounted to the hull in the Laz area - forward near the bulk head and away from the rudder. The hull needs to be solid fiberglass for this to work and it must be on the 26S because this seems to work fine. I initially tested this by using some of the toilet sealing wax (comes in a ring, seals the bottom of the toilet). Just make a good mechanical seal between the transducer and the hull with a glob of wax - work out all the bubbles. This worked but is only temporary as I know from first hand experience that freezing weather will break the wax bond. I ended by epoxying the transducer to the hull surface (JB epoxy - or something which will work on the plastic of the transducer). I have a cheap fish finder however the manual said the tranducer would work fine shooting through the hull. And it does to 100 feet, havent been able to test it past that since that is the deepest water Ive been in. I currently dont have a good reason to watch speed but if occasinally do, I just use a GPS. The PO had a big ol hole in the bottom of the boat for a worn out obsolete speed transducer which I gutted and sealed and I dont like to even think about it (dang, Im thinking about it now..),.
Answers ....
Does a transom mount work properly on a sailboat? Would my daggerboard cause turbulence and affect the accuracy? Not really as you will get a lot of turbulence from the centerboard, especially if the centerboard in not enclosed at the top and the board 'sucks air' down into the water. A sailboats hull near the tansome will usually have a lot of airbubbles that gets sucked in from the sides of the hull and exit from underneath at the transome .... a lot of air bubbles will degrade the sensitivity of the depth measurement. Can it be located so that it still functions when heeling? If mounted on or very near the centerline of the boat. When mounting off or away from the centerline you will get different speedo readings on each tack due to the flow 'streamlines' hitting the paddlewheel differently when the boat on different tacks. Putting the paddlewheel directly on the centerline will not see such differences from different tacks. Do any of you have experience with the suction cup mounting system? Not a suction cup but a 'puck mount' .... the transducer (puck) is attached to the inside bottom surface of the hull and pointing straight down through the solid fiberglass (not a cored hull). Find a flat spot well forward of the keel/centerboard (to avoid turbulence), apply a big 'cone' of silicone caulk to the hull, push the 'puck' down into the puddle of caulk carefully so that there are no air bubbles in the caulk. If not how have you mounted yours? Some transducers can work through the hull, but to get speed you need a paddlewheel which must be mounted in contact with the water. You need the wheel IN the water.
Does a transom mount work properly on a sailboat? Would my daggerboard cause turbulence and affect the accuracy? Not really as you will get a lot of turbulence from the centerboard, especially if the centerboard in not enclosed at the top and the board 'sucks air' down into the water. A sailboats hull near the tansome will usually have a lot of airbubbles that gets sucked in from the sides of the hull and exit from underneath at the transome .... a lot of air bubbles will degrade the sensitivity of the depth measurement. Can it be located so that it still functions when heeling? If mounted on or very near the centerline of the boat. When mounting off or away from the centerline you will get different speedo readings on each tack due to the flow 'streamlines' hitting the paddlewheel differently when the boat on different tacks. Putting the paddlewheel directly on the centerline will not see such differences from different tacks. Do any of you have experience with the suction cup mounting system? Not a suction cup but a 'puck mount' .... the transducer (puck) is attached to the inside bottom surface of the hull and pointing straight down through the solid fiberglass (not a cored hull). Find a flat spot well forward of the keel/centerboard (to avoid turbulence), apply a big 'cone' of silicone caulk to the hull, push the 'puck' down into the puddle of caulk carefully so that there are no air bubbles in the caulk. If not how have you mounted yours? Some transducers can work through the hull, but to get speed you need a paddlewheel which must be mounted in contact with the water. You need the wheel IN the water.
Turbulance and transducter placement
As a general rule, you want the transducer ahead of the keel and along the centerline. Your concern about turbulence and heeling are well founded. They are the chief causes of transducer error. If you can't find a location ahead of the keel then the further forward you can get them the better. The paddle wheel especially needs "clear" water to operate correctly. If you can only put one up front then the speed transducer would be better placed there. The issue with suction cupping a transducer to the stern is that unless you have a planing sailboat, the stern will "squat" as the speed goes up. This causes the transducer to get dragged through the water. Don't be afraid to cut a hole in your boat but do your homework and know what you are getting into.
As a general rule, you want the transducer ahead of the keel and along the centerline. Your concern about turbulence and heeling are well founded. They are the chief causes of transducer error. If you can't find a location ahead of the keel then the further forward you can get them the better. The paddle wheel especially needs "clear" water to operate correctly. If you can only put one up front then the speed transducer would be better placed there. The issue with suction cupping a transducer to the stern is that unless you have a planing sailboat, the stern will "squat" as the speed goes up. This causes the transducer to get dragged through the water. Don't be afraid to cut a hole in your boat but do your homework and know what you are getting into.
paddle wheel mount
Don't fall in but if possible when your boat is underway stick your hand in the water where you want to mount paddle wheel on transom. You should be able to feel the differing flows. On my boat it was very obvious where the dead water was. I ended up mounting Humminbird paddle wheel on a plastic starboard strut about eight inches below surface and about eight inches off center. When mounted too near hull it didn't work. Works fine heeled over both ways too. The strut tends to catch grass and will probably get knocked off someday, which is why I made it small and not too strong. I also shoot through the hull with the puck stuck in a gob of toilet ring wax. Works perfect.
Don't fall in but if possible when your boat is underway stick your hand in the water where you want to mount paddle wheel on transom. You should be able to feel the differing flows. On my boat it was very obvious where the dead water was. I ended up mounting Humminbird paddle wheel on a plastic starboard strut about eight inches below surface and about eight inches off center. When mounted too near hull it didn't work. Works fine heeled over both ways too. The strut tends to catch grass and will probably get knocked off someday, which is why I made it small and not too strong. I also shoot through the hull with the puck stuck in a gob of toilet ring wax. Works perfect.
With Walt...
I went thru this process too. Mounted my "In-Hull" transducer as far forward as possible/practical squished into bondo--works great for my Hummingbird "Finder", Bottom & Fish OTOH the new guts in my "Thru-Hull Mariner Knot Meter" aren't working all that well... My fault or theirs??? However, Garman-ETREC gives me Speed et al, so i think i might have wasted the cost of the new KM parts... I'd go with the "In-Hull" 'puck' & the GPS... Roger
I went thru this process too. Mounted my "In-Hull" transducer as far forward as possible/practical squished into bondo--works great for my Hummingbird "Finder", Bottom & Fish
OTOH the new guts in my "Thru-Hull Mariner Knot Meter" aren't working all that well... My fault or theirs??? However, Garman-ETREC gives me Speed et al, so i think i might have wasted the cost of the new KM parts... I'd go with the "In-Hull" 'puck' & the GPS... Roger
Love my bi-data
The advantage of using a bi-data (speed and depth) is that you get both readings from the same instrument and the response is fast. Where we usually sail we do not need the GPS on so by using the bi-data we use less draw on the battery and see the display of depth and speed at all times with no delay. I like that if I make a correction (such as let the jib out a bit) I can see instantly the impact on speed. The feedback helps you learn what works and what doesn't. I am not sure if a GPS gives that prompt a response. So, base your equipment decisions on where and how you sail.
The advantage of using a bi-data (speed and depth) is that you get both readings from the same instrument and the response is fast. Where we usually sail we do not need the GPS on so by using the bi-data we use less draw on the battery and see the display of depth and speed at all times with no delay. I like that if I make a correction (such as let the jib out a bit) I can see instantly the impact on speed. The feedback helps you learn what works and what doesn't. I am not sure if a GPS gives that prompt a response. So, base your equipment decisions on where and how you sail.
A Speedo Meter that derives its data from GPS
and displays it in large LED direct readout works for me. Selectable between MPG and KTS as well as Compass Data Coordinates to add to the mix that toggles between the two on four second intervals, makes it easy to install and more accurate that old mechanical paddle wheel transducers. Now if someone would just market that at an affordable price! Tom
and displays it in large LED direct readout works for me. Selectable between MPG and KTS as well as Compass Data Coordinates to add to the mix that toggles between the two on four second intervals, makes it easy to install and more accurate that old mechanical paddle wheel transducers. Now if someone would just market that at an affordable price! Tom
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