How important do you find a 'speed through water' reading.

[markbarendt]

or this:
Until the mid-19th century, vessel speed at sea was measured using a chip log. This consisted of a wooden panel, attached by line to a reel, and weighted on one edge to float perpendicularly to the water surface and thus present substantial resistance to the water moving around it. The chip log was cast over the stern of the moving vessel and the line allowed to pay out.[6] Knots tied at a distance of 47 feet 3 inches (14.4018 m) from each other, passed through a sailor's fingers, while another sailor used a 30-second sand-glass (28-second sand-glass is the currently accepted timing) to time the operation.[7] The knot count would be reported and used in the sailing master's dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, or 1.85166 km/h. The difference from the modern definition is less than 0.02%.

I actually want to do this with the grand kids sometime.

 

[markbarendt]

Here's a pic from a Steve D article of a manifold off a sea strainer. He cautions it must be properly supported. I'll further state the obvious - the sum of the outlets should be well under the inlet as measured by the area of each hose (pi x r^2). This is balanced by hose run which on most trawlers is fairly easy due to central location of the engine room.

As mentioned, to me the big benefit is consolidation of sea strainer. Many A/C installs have a dedicated through hull with a puny plastic sea strainer placed inconveniently. Groco also makes a check valve that often get used in A/C inlets to prevent loss of prime, but used judicially, can assist in contention between out demand.

https://www.groco.net/products/valves-seacocks/check-valves/pnc-series

Groco also manufactures this handy manifold outlet in a couple different sizes. Idea would be to put it on outlet of an existing sea strainer. If you read through the entire description, they actually do not recommend it - liability concerns I suppose.

https://www.groco.net/products/fittings/manifolds/raw-water-manifold

I am told that new engine manufacturers require a dedicated thru hull or they will void warranty.

Peter



View attachment 111616

Thanks

 

[OldDan1943]

I actually want to do this with the grand kids sometime.

I think that's against the law???

 

[markbarendt]

I think that's against the law???

On second thought, maybe the dog is a better choice.

 

[OldDan1943]

On second thought, maybe the dog is a better choice.

Nawww, the dog is very important.

 

[ak-guy]

Coming alongside cruise ships for many years STW was very important to us. The pilot boat and cruise ship interaction was optimum at 6-8 knots. We used a paddle wheel for many years but switched to Airmar Ultrasonic. It was much more reliable and accurate. We operated in an area with lots of current and it was important for us to know STW when talking to pilots on the ships. We would never disagree with them on the radio, only state what our gauge was reading and ask that they speed up or slow down a little.

 

[Hippocampus]

A-G interesting to hear your Airmar ultrasonic was more accurate. Ours was accurate but had several fail in succession so went back to a paddle wheel. That was in 2013-4 time frame. Seem to recall 4500 as the model. Do you recall the details of yours?. We ran it through an ITC-5 but had other instruments running through that which worked faultlessly so pretty sure that Airmar unit was a POS. Airmar was kind. They kept shipping me new ones at no cost but I got fed up and bought a paddle wheel which was 100% reliable. Also didn’t like that with any turbulence or foam in the water the ultrasonic wouldn’t give you a reading so mostly worthless when it was bumpy.

 

[ak-guy]

A-G interesting to hear your Airmar ultrasonic was more accurate. Ours was accurate but had several fail in succession so went back to a paddle wheel. That was in 2013-4 time frame. Seem to recall 4500 as the model. Do you recall the details of yours?. We ran it through an ITC-5 but had other instruments running through that which worked faultlessly so pretty sure that Airmar unit was a POS. Airmar was kind. They kept shipping me new ones at no cost but I got fed up and bought a paddle wheel which was 100% reliable. Also didn’t like that with any turbulence or foam in the water the ultrasonic wouldn’t give you a reading so mostly worthless when it was bumpy.

I have been retired for a couple years and the boat we used has been retired. All I can say is it worked for us. The transducer was probably purchased around 2015. Also we didn't experience any turbulence problems. There is a lot of variation with different hulls and transducer placement.

 

[markrkrebs]

I want one

I don't have one and don't miss it. In my mind, it's an occasional nice to have, but not at all necessary.

I miss my knot log. Not really a through hull as the hole is fully filled so don't be afraid of it.

On the others, I've once been almost sunk by a siphon through a gray water fitting. A duck valve on the shower sump failed open. I heard it gurgling before heading off.

Bilge pumps would've kept up. Probably.

How was that Ever ok? It's a lesson in not trusting the setup you inherited.

 

[mikecambrai]

how-important-do-you-find-speed-through-water-

Over 60 years I have used most of the systems for measuring speed through the water from Pitot tubes to impellers to screws rotating via a cable to the instrument and even setting and towing a Walker log.
Now I have the Sumlog which works intermittently, but the easiest is my NASA Speedo which tells me speed over the ground via a GPS mushroom screwed to the deck. Cheap and cheerful, but tells me all that I need for navigation (SOG) and cannot get confused with weeds and other garbage below the waterline and does not need a hole in the hull to fit it. I avoid any holes in the hull if at all possible.

 

[rgano]

There we go, trolling for fish is something I had not thought of.

But if you know what speed your trolling RPMs develop in still water, a simple glance at the SOG and a split second of head math will tell you what water speed the lures are experiencing.

I had my trawler a very long time before I installed a Humminbird sounder with option for a paddle wheel transducer. It always worked well because it had the option to be pulled into the hull which is where it resided when not underway.

I will not be installing any such device in this Mainship. Not needed.

 

[tdoriot]

Composting toilets?? I gotta say, that idea give me a bit of the old "throw up in my mouth" thing.

 

[CarlF]

I have had friends with the Airmar ultrasonic. None have found it more reliable than the paddle wheel. (the sensors foul)

But I'll put in another vote for the Airmar DST 810. One hole for depth, speed, and temp. The thru hull has a spring baffle that snaps closed when you pull the sensor to clean the paddle wheel. Just a trickle of water comes in. Very easy to do (although be sure to place it somewhere that's easy to reach - likely directly below a cabin sole lift out).

Without STW you have no idea of current or drift which in areas like Maine where currents are driven by 10ft tides is pretty important.

On another note, you mentioned fancier sonar. Did you mean the forward looking sonar? While these might be useful to look for fish, I found the very expensive Garmin Panoptix PS51 completely unhelpful for what I wanted - warning of upcoming rocks or shallows.

The problem is that these can only see forward about 8-10 times the depth of the water (says so right on the Garmin web site but it didn't register when I was ordering it). So if you draw 5ft and are looking for a 4.5ft shallow, you only see it 40ft before you hit it. Not many boats can stop in one boat length. And that assumes you are staring at the screen 100% of the time instead of looking where you are going.

But they are fun to show some one your anchor chain - once or twice.

 

[Capt Ray]

Lots of good thoughts shared by the group. I've learned from most.

The only thing I can add is that we took delivery of a Mainship 390 in July, whose fouled paddle was removed and a "cap" was in place over the through hull fitting. (It was clear that this was not deployed in years. It's through hull transducer for depth was still working fine.)

The thing that bothers me most is the whole assembly is all made of PLASTIC, including the through hull fitting (no valve, only a screw on plastic cap)... obviously below the waterline.

I consider this the most vulnerable point of failure on my boat, and plan to replace the through hull with a bronze fitting with valve, and discard the paddle sensor in the nearest dumpster. (I keep wood plugs close at hand!)

Since the hole is already there, I might consider removing the plastic through-hull fitting with a forward facing Panoptix transducer by Garmin, which looks to be of better materials... though my research is not finished yet.

Ray
Shellerina.com

 

[EngNate]

I will add STW when I get around to it. Running around the BC central coast, over many of the same routes again and again, I'll use the real time observations in future planning. There's no current atlas for up here, no published info or others' observations on the patterns like can be found for the south coast. (Maybe somebody knows of some writings?). There's that, sailing, and salmon trolling, and that's all the use I can see for it.

 

[Captain K]

Knowing speed through the water (STW) is one of those lovely essentials mostly lost to our modern GPS/chartplotter world. Way back when, STW was useful in evaluating current. In fact, STW was the only thing mariners could measure directly using the old speed log with knots in a line, or the more recent taffrail log. These days few know how to calculate, or to compensate for current. Put all that down to the ravings of an old man who has spent far too much time with Duttons, ha! Plug that hole my friend, you'll never miss it. Cheers!

 

[Sharpseadog]

For the past 40 years I have always had a transducer with STW paddle wheel in both our sailboats and our current trawler. Knowing the difference between STW and SOG is extremely helpful where I boat. I operate in the San Juan Islands and Canadian Gulf Islands where there are huge variations in tidal current speeds and direction in the channels between islands at any given time. Yes there are ways to estimate current speeds, but I've found the STW very helpful in saving fuel by keeping boat at optimum hull speed. The fuel consumption curve is far more dependent on water speed than the extra fuel and power needed to overcome strong head winds and seas. So if I'm bucking strong headwinds and seas, I increase RPM enough to maintain my 7-1/2 kt hull speed, but fuel consumption doesn't go up exponentially like it would maintaining SOG speed against strong head currents which would put boat over hull speed, sometimes by a lot, with a very heavy fuel penalty. Yes, there are times when you might actually save fuel blasting through a narrow channel against a strong current, but that's a judgement call and having STW data visible on my plotter right next to SOG is very useful. [emoji569][emoji569][emoji924][emoji4]

 

[psneeld]

Amateur boater, sailor.....used to use STW before GPS....rarely since.

Commercial mariner since 1999, all kinds of commercial operations...never found a need for STW as it was easily calculated in my head from GPS info and chartplotter info.

I can see why some like it...but totally unnecessary to perform almost any function on the water that I have ever done.

From sailing, to coming alongside vessels, to towing.... to easy to guess from SOG.

 

[AlanT]

I find it pretty useful. I like to know the angle of my drift, which I can see by enabling current arrows on my chartplotter. I find this really useful when teaching my children, and now my grandchildren, why they don't always wind up where they point the boat. Once they understand the relationship between the arrow and the boat they start looking for eddys and pretty soon can identify favorable eddys which makes for a more interesting, and faster, passage.

I must admit as a former sailor and paddler I have always been fascinated by current, I also appreciate it may be irrelevant to many.

The route from my boat's marina to the community dock in my neighborhood takes me through the Tacoma Narrows, with peak currents of up to 4 or 5 knots so every bit of assist helps.

~A