Bronze vs Marelon Thru-hulls

tommays · Sep 28, 2010

On my Cal 29 (1970) the bronze thru-hulls are flush and in good shape on the ones i removed BUT they are larger than anything you can buy new except the marlon flush mounts

So if they were bad i would have to use marlon or do soem glass work

My 1970 boat has a bonding wire going from the chainplates to all the thru-hulls and shaft strut ,The boat never spent much time on shorepower and BAD shorepower seems to be one of the bigger problems

woodster · Sep 28, 2010

i am replaceing all the through hull fittings on my boat with bolted sea cocks (bronze)below the water line.... with bronze through hull exit fittings and sealing them with 5200 sealent.....as for the ones above the water line i am also replaceing them with new plastic through hulls.....if you feel the need to put shut off valves on the above water line holes then marelon would be ok ...some use them below the water line as well but i am not to fond of the arrangement ....sence you have the boat out of the water anyway it may be best to excersize caution in your selection of plumbing hardware as it costs a lot to haul out to correct a insuffent choice.......hope this helps ........

regards

woody

Steve Dion · Sep 28, 2010

Woody:

I am curious on why you think you need 5200 to bed your seacocks. The "general consensus" is not to use 5200 for ANYTHING other than a deck to hull joint or keel to hull (something that would not normally be taken apart in the future.

There is no guarantee that you would NOT need to replace one of these in the future. If/when you do you may be looking at damage to the hull.

Steve Dion · Sep 28, 2010

Unless there have been major changes to the handles on the marelon valves, they really do not instill much confidence in their strength.

Make mine bronze!

woodster · Sep 28, 2010

Steve Dion said:
Woody:

I am curious on why you think you need 5200 to bed your seacocks. The "general consensus" is not to use 5200 for ANYTHING other than a deck to hull joint or keel to hull (something that would not normally be taken apart in the future.

There is no guarantee that you would NOT need to replace one of these in the future. If/when you do you may be looking at damage to the hull.

Steve i took out some old seacocks out of a 1984 Allmand 35 this past year and replaced them with new ones using 5200 about 8 months ago....then my buddy decided to go with a water cooled refer unit witch i just put in last week, and had to remove the drain seacock and install the new fitting ....in doing so i found that i had a very good gasket seal in the 8 month old one ...yes it was a little tough getting it off but i liked the fact that the 5200 made a very good gasket after sitting for 8 months.....that 5200 is good stuff...even though it may be a little over kill i feel that below the water line it is the best for that application......i also champhered the hull to the out side to insure that i created that gasket .........

regards

woody

obtw i am very impressed with the refer unit

Bill Roosa · Sep 28, 2010

Bonding and metal vs glass reinforced nylon

The latest thinking is to unbond everything but to tie the engine ground, DC electrical ground, AC electrical ground and Radio grounds together. WM has a great document on their advisor pages covering the details.
Course if you us reinforced nylon you don't even have the issue of bonding the thru-hulls. They don't rust either. Course they do burn but if you are getting them that hot you have a host of other troubles and perhaps a hole in the boat would be a good thing at that point.

Steve Dion · Sep 28, 2010

Woody:

I am very impressed with ours (IsoTherm SP Refrigeration). I wish I could determine the actual power usage, but I do not have any monitoring equipment.

There were a couple of different things that drew me to these units. First my friend Steve Weinstein had one on his H'33. He kept his boat on a mooring and was able to keep the unit running 24x7 with just solar panels.

Another thing was the fact that there was no fan or heat inside the cabin of the boat. The coolant runs thru the thru-hull fitting to discharge the heat and only the pump that pumps the coolant is needed to power the system.

We have had ours for 3 years and I sometimes forget that it is even there.

I am glad you like the system.

John Nantz · Sep 28, 2010

If it were my boat I'd definitely go Marelon

And avoid all the problems that bronze causes.

1. No grounding required,
2. No corrosion,
3. No electrolysis: even if you don't have electrical problems on your boat, there can be a "hot" boat nearby that can cause real problems!.

This reminds me about a guy I met in the boatyard several years ago who was fixing his Columbia 50 to head off to the South Pacific. Turns out his bronze strut broke off while he was working on the prop. It looked fine on the outside but the metal below the surface was all corroded.

The Marelon valves on my '88 boat are still working fine after all these years.

White plastic above the waterline is subject to UV degradation and it would be a good idea to replace it every so often. My experience is that the plastic will last quite a long time, though.

Steve Dion · Sep 28, 2010

John:

That reminds me of the fellow that had the S.S. strut break. This strut was a replacement for the bronze one that came with the boat. I suppose that regular maintenance of the zincs would help prevent this type of failure, but even that may not be an absolute solution.

We live in fresh water and do not experience much in the way of zinc deterioration.

John Nantz · Sep 28, 2010

Marina "hot boat" experience

Our marina has a policy of checking incoming boats for length, width, and "potential" before they are accepted for berthing. We have a group who has come up with equipment and a system for checking hot boats.

A few years back there was a transient boat (or at least it became transient) that was in the marina for a very short time. During that time it caused a lot of damage to neighboring boats due to it's electrical problems. I never really learned about all the details but there was some expensive damage to low-drag props, for example. These props can cost a couple thousand and up so damage to them can be expensive.

Who knows what else in the way of damage was caused to things like struts, through hulls, engine bearings and the like.

I'm a stickler for having my zincs changed on a regular basis, standardly about 4 months, whether they need it or not. One good thing about checking them regularly is if something like this happened then you'd know about it sooner.

RonRelyea · Sep 28, 2010

Re: Marina "hot boat" experience

"We have a group who has come up with equipment and a system for checking hot boats."

John ... can you elaborate on your equipment and system for hot boats? Maybe in a new post to keep from hijacking this one??

THANKS!

FastOlson · Sep 28, 2010

And the Answer is: __________

Steve Dion said:
Unless there have been major changes to the handles on the marelon valves, they really do not instill much confidence in their strength.

Make mine bronze!

Drastic changes to the design already happened. Redesigned about 2000. I changed from the old style on our '88 model boat to the new ones. No problems.
Some of our original ones were very stiff.

Between good quality bronze with ball valves and the newer Forespar Marlon, the best choice is..... either!
Note that if you fear electrolysis, you want the Marlon fittings.

But really, no wrong answers.

Bonding. My oh my. Religious fervor on all sides. We do not have it and I do not personally know any surveyors that like it, but still..... some folks swear by the idea.

Good backing plates -- there's something we can all agree on!

Cheers,
L

FastOlson · Sep 28, 2010

And the Answer is: __________ !

Steve Dion said:
Unless there have been major changes to the handles on the marelon valves, they really do not instill much confidence in their strength.

Make mine bronze!

Drastic changes to the design already happened. Redesigned about 2000. I changed from the old style on our '88 model boat to the new ones. No problems.
Some of our original ones were very stiff.

Between good quality bronze with ball valves and the newer Forespar Marlon, the best choice is..... either!
Note that if you fear electrolysis, you want the Marlon fittings.

But really, no wrong answers.

Bonding. My oh my. Religious fervor on all sides. We do not have it and I do not personally know any surveyors that like it, but still..... some folks swear by the idea.

Good backing plates -- there's something we can all agree on!

Cheers,
L

kloudie1 · Sep 28, 2010

I have a mixture of marlon and bronze all are over 20 years old and all are fine. The Marlon ones are 2, 3/4" ones. The bronze ones are 3, 1 1/2" and one 3/4".. My experience is that I don't use use a bonding wire on the bronze ones.. but the strut probably does need a bonding wire. This on my boat with a standard cell reference survey ..

Hermit Scott · Sep 28, 2010

I bought my boat 2 years ago. I started fixing it from the bottom up. Through the advice of trusted members on this site, I replaced all the through hulls below the water line.
I used bronze through hulls, flange adapters(VERY important) and bronze ball valves.
With the flange adapters you can unscrew an old or damaged ball valve and screw another one on with out a problem while in the water.
Check out this site http://www.pbase.com/mainecruising/replacing_thruhulls
This is the method I followed when I replaced my through hulls.
The only deviation I did was coated the outside throughhull and as far as I could get my finger into the hole with epoxy with colodial silica mixed in. I did this so no bottom paint would touch the bronze.
I follow the school of not bonding anything. I read some books, looked at opinions on here and elsewhere and decided to have nothing bonded.
One of the best things I did to my boat was install really good seacocks. It really lets me leave the boat with the confidence that when I return it will still be floating.

druid · Sep 28, 2010

One thing about Marelon: it's hard to tell if it's marelon or cheap plastic - EVERYONE can tell bronze when they look at it.

But then, don't go by ANYTHING I say: the way I install thru-hulls is to epoxy them in - if they need to be replaced I can cut them out and re-glass. I can't STAND bedded thru-hulls that move when you try to tighten the clamps...

druid

Hermit Scott · Sep 29, 2010

Mark Ferrick said:
of you folks for responding. I will go with bronze, and only bonding my strut ( once I replace it. It broke and around the weld, it looks like pink clay. ) All my other thru-hulls appear to be ok.
One set of decisions done with. thanks.....................

Mark, if you want to protect your strut, put a zinc on it. I don't understand "only bond your strut", are you going to bond it to something else?