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

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Thank you for all the input y’all. Going with two bilge through hulls. For speed through water I do believe I’ll be making a rpm table.
 
Lou_tribal said:
Cruising on rivers I like to know current speed, just to learn where the current is stronger/weaker. Is it essential? No.
Now with experience with my boat I know its speed when no current at given RPM so not really need it.

L
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Usually srtonger on the outside of curves and weaker on the inside. I have found that to be good enough for my work.
 
markbarendt said:
Thank you for all the input y’all. Going with two bilge through hulls. For speed through water I do believe I’ll be making a rpm table.
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Good decisions, Also re think sharing a thru hull for the engine with anything else. I was getting ready to say that an rpm table will tell you the speed through water no matter which way the current is flowing if taken in still waters with SOG GPS.
 
Even a hand held GPS usually has an arrival time function , about all I need.
 
In addition and background to the comments I've already made, one of my enjoyments in boating is observing the natural world around me, and comparing it when I could to the man made theoretical world of charts, chartplotters, tide predictions, and so on. Also, the effects of those natural forces on the boat and other things floating on or near the water. I even got a kick out of looking at the STW while at anchor for various reasons.

If you are boating with the mere purpose of getting to Point A from Point B, I suppose a lot of things are not "necessary". I note the comment about carrying a lead line, something I also found fun, if only to grease it up and see what the composition of the bottom was.
 
I have a complete Raymarine setup, including MFD, sounder, VHF, auto-pilot and STW paddle wheel. I find the data it (generally) produces useful because I like to better understand the current -- especially when running at slow speeds on electric. Like others have mentioned, however, the paddle wheel is prone to hanging due to algae, weeds, etc. I find backing down can sometimes free it up. More often, however, crashing through some rough seas is what is usually needed to free it up.
 
I have a door next to the helm, so no need for a through hull, paddle wheel, electrical connection and gauge. Just spit over the side. Extremely accurate.
 
Can anyone list the reasons one would want to know speed through the water? I can’t seem to think of any scenario where I might use this information.
 
In Jacksonville. maybe of little use. Where there are substantial currents, it can be of use.

A note on GPS: It is almost absolute in accuracy. Now the receiver's calulation and display may be off by a small or large amount. That's on the receiver, not the system.
 
Still think 6 to 8 kts. is 6 to 8kts. Sail or power. So gaining a tenth or full knot is meaningful on anything over a day trip coastal or blue water. So for a full displacement hull a Speedo is good to have. If you don’t trust plastic they still make bronze. They install a whole lot of marelon through hulls. Anything if not maintained can fall.if that’s your worry buy metal and put in stand pipes or put your instruments inside a sea chest.
 
Hippocampus said:
Still think 6 to 8 kts. is 6 to 8kts. Sail or power. So gaining a tenth or full knot is meaningful on anything over a day trip coastal or blue water. So for a full displacement hull a Speedo is good to have. If you don’t trust plastic they still make bronze. They install a whole lot of marelon through hulls. Anything if not maintained can fall.if that’s your worry buy metal and put in stand pipes or put your instruments inside a sea chest.
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There's one big difference between sail and power though. With power, if you're at a given RPM, your speed through water should be fairly constant against current. Wind and seas will affect it some though. With sail, you don't have that kind of reference point, so you have a lot less to go by for estimating STW vs SOG without a direct STW measurement.
 
Have used Fort Lauderdale Speedo in the past to calibrate and rebuild tachs. They do a great job. Give them +1 if you need that work. Never the less for kicks and giggles did a chart comparing stw to rpm. At least in my experience there’s a fair bit of variation between the two. Think you’re right it’s due to wind and seas. Several of my friends on sail have also decommissioned their speedometers. It obviously not a key reading for many and not of interest to them. Does your AP require stw?
 
An extra hole in the bottom?
No thanks
Two through hulls is enough for us.

RPM gives xx knots of speed
+ or - that is current.
That's all we need to know.
 
markbarendt said:
Thank you for all the input y’all. Going with two bilge through hulls. For speed through water I do believe I’ll be making a rpm table.
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The RPM table will be a fantastic idea, making note of wind and sea conditions, fuel and water loading.

Each 1000 rpm, measured mile out and back maybe twice or 3 times?
If you have a gph meter, you can actually graph it and quickly pick out your 'sweet spot'. Dont be surprised when you graph it and your 'sweet spot' is between 7 and 8 knots. LOL

Depending upon your desired detail, you can occupy a couple of days doing this.

When you get all this done, you are making turns for 7 knots and your SOG is 5 knots, you are running into a 2 knot current. SMILE
 
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Woodland Hills said:
What power does this information give me? I can’t think of any, can you?
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Must be something from The Power of Greyskull :D

He-Man-saying.jpg
 
My rpm table consists of 1750 rpms is 6-3/4 kts. If gps says 6-1/4 kts, theres a half knot of wind or current against. Etc.

Speed through water was useful when there was no alternative so you needed it for dead reckoning. I'm with Woodland Hills on this one.

I have a bunch of above waterline thru hulls. Fewer are better but I don't really care. Bilge outlets should absolutely be dedicated with a vented loop of course.

Seacocks are incredibly reliable so not sure why the concern about holes in boat. That said, I've gone to oversized intake manifolds not because I'm trying to reduce holes, but I want to reduce sea strainers and make sure valves are accessible.

Peter
 
Put in a sea chest and reduce the through hulls and you can stare at the bottom too LOL
Hey, put an IR camera on top the plexiglass sea chest cover and you can watch the bottom from the helm!!!
 
There are ways to work around knowing the speed thru the water as it relates to adjusting your course for current and drift. This would not apply if going off shore and out of sight of land.

I just adjust my course by observing on my chart plotter that the "predictor line" is pointing where I want to end up, than set the auto pilot on that course. When you look out the front window you may see you are no where close to steering a direct course to your destination because of the current, but you will end up where you want to be.

I use this all the time when crossing the Strait of Georgia and Queen Charlotte Strait where it is 20-30 miles across and you can't even see where you want to end up. But the predictor line shows me I will end up where I want to be.

As far as fishing goes (salmon fishing up here), I just watch my line angle on the down rigger, not so much the speed on the GPS. If I have the line angle correct, my speed will be right too.
 
Woodland Hills said:
What power does this information give me? I can’t think of any, can you?
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It's possible my forty years of sailboat racing and a total focus on dozens of variables and adjustments , all quantified by STW has me maybe attaching too much importance to this measure when all I have to do with my trawler is thump a lever if I sense a needed speed adjustment in the seat of my pants.

By the way , I am totally over the years of screwing with paddle wheels and I'm not going to do that on my trawler. But... there is a hole in my bottom where an old paddlewheel used to live and soon as I see a decent deal on a N2K speed device that works WITHOUT a paddlewheel and fits that hole I'm going to buy it and I'll pay some extra if it will tell me water temp because I'd like to know that also. Furthermore as soon as I have an extra boat buck with nothing more important to spend it on I'm installing a masthead wind instrument. I would love to have all that information .

So I guess instead of why do I want that information it's more like why wouldn't I want more information about the environment I am operating in.

Information is power, just ask Google !
 
mvweebles said:
My rpm table consists of 1750 rpms is 6-3/4 kts. If gps says 6-1/4 kts, theres a half knot of wind or current against. Etc.

Speed through water was useful when there was no alternative so you needed it for dead reckoning. I'm with Woodland Hills on this one.

I have a bunch of above waterline thru hulls. Fewer are better but I don't really care. Bilge outlets should absolutely be dedicated with a vented loop of course.

Seacocks are incredibly reliable so not sure why the concern about holes in boat. That said, I've gone to oversized intake manifolds not because I'm trying to reduce holes, but I want to reduce sea strainers and make sure valves are accessible.

Peter
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I agree that seacocks are very reliable. Like you I want good access.

On all the boats we looked at before buying, and all the club boats we sailed on, access was really tough for a truly significant percentage of the valves. It also seemed that invariably, the valves that were toughest to get at were frozen or nearly so.

When jobs are tough, they don’t get done as reliably. If for no other reason than maintenance I want good easy access in one general area of the boat where all the valves can be easily seen.

What I don’t want is to be to digging out everything under the sinks in the heads to shut one here and one there and then hunting through the four corners of the engine room to find the other 11.
 
markbarendt said:
.

What I don’t want is to be to digging out everything under the sinks in the heads to shut one here and one there and then hunting through the four corners of the engine room to find the other 11.
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So get rid of them

If we can have two on a two shower, 6 sink, 2 toilet, 1 main engine, 1 genset, 1 deckwash 60 fter surely you can.
 
markbarendt said:
I agree that seacocks are very reliable. Like you I want good access.

On all the boats we looked at before buying, and all the club boats we sailed on, access was really tough for a truly significant percentage of the valves. It also seemed that invariably, the valves that were toughest to get at were frozen or nearly so.

When jobs are tough, they don’t get done as reliably. If for no other reason than maintenance I want good easy access in one general area of the boat where all the valves can be easily seen.

What I don’t want is to be to digging out everything under the sinks in the heads to shut one here and one there and then hunting through the four corners of the engine room to find the other 11.
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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



Screenshot_20201220-063229.jpeg
 
Electronics, huh. You guys forget the old fashioned way to measure your speed.. just mark various speeds on your deck. The location of the rear crest of your bow wave tells you how fast you’re moving. I did that on a previous boat and it was really cool. Great conversation piece with guests.
 
mvweebles said:
Here's a STW instrument that requires no hole in boat.

https://www.1stdibs.com/furniture/m...VwbiGCh11swfmEAQYBCABEgLgvPD_BwE&gclsrc=aw.ds
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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%.
 
Simi 60 said:
So get rid of them

If we can have two on a two shower, 6 sink, 2 toilet, 1 main engine, 1 genset, 1 deckwash 60 fter surely you can.
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I agree. I do think all the technical details can be addressed to make it safe.

This is going to have to be a phased plan though. We’re going to get rid of a bunch of the valves this winter and get the leftovers corralled into the front end of the engine room, port and starboard and in full view.

The remaining valves will be Marelon so we can stop worrying about the metal bits falling apart.

I was a fan of Marelon before this boat but got fully sold as we have been cleaning and hunting through all the nether regions in this boat to find all the bits and bobs and gremlins.

The very last through hull we found was hidden on the outside by the mostly gone leftovers of an oyster (after a pressure wash) and inside by a pair of hoses running from the engine to the water heater and the left over 5 gallons of bilge water. The bonding wire post on the metal cap had corroded through with the bonding wire now laying aside.

This was an old abandoned hole just waiting for the least appropriate time to make my life miserable. If we had been rushing things we could have easily missed this.
 
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