Advice on These Thru Hulls From Raymarine

[jtsailjt]

Originally Posted by Trawlerman

As I have previously commented in other topics, I really wonder why anyone in this day and age would want a water-speed sensor. GPS is so accurate these days and has the advantage of true speed-made-good over distance, which for planning time-to-go to destination is a must have.

I want a water speed sensor so I can tell just how fast I’m moving through the water. If I tack and my GPS speed is .5 kts lower than it just was on the previous tack, without a water speed sensor I have no way of knowing whether it’s because there’s a current, or perhaps I need to adjust my wind angle or check my sail trim. GPS is great for planning purposes and navigation, but it doesn’t tell the whole story if you’re concerned about sailing performance.

Of course modern airliners are all equipped with multiple GPS’s, but they’re flown by reference to their speed through the air rather than speed over the ground for similar reasons to why sailors care about speed through the water.

No need to wonder any longer! [emoji4]

[noelex 77]

Originally Posted by Jubilee39

You missed the point completely, If plastic thru hulls are good enough for metal boats why would one want to go to the expense of metal thru hulls. I personally have installed many thru hulls on metal boats. There might be a nipple welded on the hull and the plastic fitting screwed on to it. rarely would you place the actual valve above the waterline, where is the waterline when the boat heels.

With respect, I don’t think I did miss the point. Metal seacocks are not possible on an aluminium boat. Unfortunately, Marlon seacocks somewhat compromise the excellent impact resistance of these hulls, which is why most premium manufacturers of offshore boats raise them above the waterline. Manufacturers such as Garcia, KM, Boreal, Alumarine etc all manufacturer yachts in this way. Others such as the steel Nordhavn favour sea-chests (basically large standpipes). In other words many manufacturers of metal offshore boats feel plastic seacocks below the waterline are not good enough although personally I feel Marlon seacocks on a fibreglass boat are an OK solution.

As well as improved impact resistance, when using standpipes the seacock can be serviced or replaced while the boat is in the water and in most instances the intake can be cleared of an external blockage by using a rod from the inside without any risk of water intrusion. If the seacock leaks or a hose pops off the seacock there is no fear of sinking the boat. There are many advantages and I am surprised that if you have personally installed many thru hulls on metal boats you have not used this system.

[wingssail]

Originally Posted by MicHughV

Since the advent of GPS, chartplotters, etc. the use of a speed sensor is somewhat moot.

Most hull speed sensors come with a "plug" in the even the sensor is removed.

Were it me, and this is my modi operandi....I just leave the plug in and fugetabout the speed sensor. In the past, I have tired of diving aboard to clean that little paddle wheel.

With the advent of GPS, I see little use for it.....but that's just me.

This depends on your feeling about what accuracy you want from your wind instruments and what information about any current or tidal flow you are experiencing that you want.

Any calculation of true wind speed and direction (as opposed to apparent wind speed and direction) needs boat speed input.

Many people are satisfied with GPS speed and most wind instruments can be configured to use SOG and COG for that input.

If you want the most accurate calculations however you'd need the paddle wheel (or some other type of water speed sensor), and if it is a paddle wheel, you need to keep it clean.

With water speed and GPS information your navigation system can also compute the tide or current, which some think is useful.

I am about to replace my water speed transducer and it will be in a plastic AirMar through hull. I think there is very little chance of anything hitting either the inside or the outside portion with enough force to break it off so I am willing to take that chance.

My new depth sounder will shoot through the hull, (I've tested it) so no danger there at all.

[Matt Johnson]

Reminds me of something I always found odd when I'd see someone installing new flanged seacocks. They'd spend tons of time/cost retrofitting their boats with those, yet they'd inevitably have a transducer thruhull that was of no concern regardless of material used.

[jtsailjt]

I actually prefer Marelon to bronze for thru hulls unless they’re in a location where something inside the boat can hit them hard enough to crack them or they’re long enough for a significant moment arm to be present. I’ve found Marelon to be extremely strong, and especially in compression, which is the type of force that is exerted by the boat running into something. In addition, with this type of impact the Marelon fitting is supported by the surrounding hull it passes through. I have managed to accidentally crack a Marelon fitting by over tightening another fitting I was screwing onto it. I was using a big wrench and needed just one more 1/4 turn for it to align properly, but it broke instead. That’s because the strong force I was exerting on it put part of the fitting in tension as well as torsion. But that doesn’t happen once the fitting is installed. The great advantage to Marelon is that it’s inert and it’s strength will never be affected by galvanic corrosion. But for a thru hull located where something inside the boat could hit it hard enough to create a strong shear force, I’d prefer bronze. My speed transducer is located in a spot that the worst thing that might happen to it is someone stepping directly on it but that would only exert a force in compression. The location and surrounding fittings protect it from any impact that might cause a shear force and it doesn’t extend far enough inside the boat for any significant moment arm to become a factor like an unflanged sink drain thru hull might. So, both bronze and Marelon have their place, depending on purpose and location. For the OP’s purposes, I think he’d be better off to stick with his Marelon thru hull for his new speed transducer.