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Old 02-03-2017, 11:41 AM   #1
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On a semi displacement barnacle fouled hull, how much slower?

I know a planning hull a lot slower than semi or full.
I would think a full displacement which already moves more slowly, it won't have as much affect as a planing hull but still noticeable.

Anyone have observations they can share?

What % drop in speeds would you think for each type hull if hull is fouled but prop is clean?
What % increase in fuel usage?

My semi-displacement hull is somewhat fouled, I am onto my 3rd year, I splashed in fall 2014.
I have been thinking to haul spring 2018.
When the water warms up, I want to get under there and clean off as much as I can.

Thinking good gloves, a flat hull scraper like what you normally use when hauling out, mask and a hood to protect my head.
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Old 02-03-2017, 11:44 AM   #2
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Could be 4 knots at WOT.

There's such a wide range of potential fouling it could be less that 4 knots.
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Old 02-03-2017, 11:47 AM   #3
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Do you think 4 knots max speed? or 4 knots drop from your normal top speed?

Over the years, regardless of fouling the boat always can do 4 knots. It is just not able to get the speed up when fouled.
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Old 02-03-2017, 11:51 AM   #4
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Not answering your question at all, but if your bottom is fouled now, I wouldn't wait for over a year to address it. At the very least I would have a professional diver clean the bottom then do it regularly on a schedule. If the diver can't clean it, then I would haul it this year, take care of the bottom, then have a diver clean it on a schedule.

Another question that doesn't help your initial question at all (sorry), have you checked changed your anodes in the past three years? That is another reason I use a diver (and the fact that my water is just too damn cold).
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Old 02-03-2017, 12:10 PM   #5
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Not answering your question at all, but if your bottom is fouled now, I wouldn't wait for over a year to address it. At the very least I would have a professional diver clean the bottom then do it regularly on a schedule. If the diver can't clean it, then I would haul it this year, take care of the bottom, then have a diver clean it on a schedule.

Another question that doesn't help your initial question at all (sorry), have you checked changed your anodes in the past three years? That is another reason I use a diver (and the fact that my water is just too damn cold).
Our summer water temps can get into upper 80's.

Have not checked any anodes. There are 4 under there.
I am also wondering about switching to aluminum anodes.

I always have replaced them at haul outs, and typically my hauls are on a 4 year schedule.
Typically, the rudder anodes are there but wasted, and the shaft anodes loose or gone as in completely missing.

What I have done with the underwater metals on my last haul in 2014.
I first paint with zinc chromate primer all the running gear.
Then I coated - smeared a thin layer of a waterproof polyurethane over all except the shaft.
I used Loctite S30 polyurethane. It is smooth enough to cover with a thin layer.

Then bottom paint all of it.

My thinking is keep the water away from the metal and the chance for corrosion goes way down. I don't ever see any metal disintegration-pinking etc...

Another thing I wonder is, barnacles have bases they attach to metal. Those bases keep the metal dry away from salt water, so barnacle bases may actually help preserve the metal.

A prop edge, the barnacles get worn away, so prop edges can dezincify I suppose easier as they are exposed to the salt water..

So I am curious how the zincs are doing this time.
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Old 02-03-2017, 12:16 PM   #6
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My 40 Albin (SD but closer to the FD curves than planing) severely fouled dropped about 1/2-1 knot at cruising RPM..with medium barnacles on hull and 6 inch or more soft growth...lots falls off when getting underway, but not all.


So 6.3 knots to around 5.5 or so....Medium growth( some banacles and pretty solid but shorter soft stuff) and I hardly noticed.


I didn't do a cruise with it like that...but some runs up and down in front of the marina to shake some stuff off.
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Old 02-03-2017, 12:26 PM   #7
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Our summer water temps can get into upper 80's.

Have not checked any anodes. There are 4 under there.
I am also wondering about switching to aluminum anodes.

I always have replaced them at haul outs, and typically my hauls are on a 4 year schedule.
Typically, the rudder anodes are there but wasted, and the shaft anodes loose or gone as in completely missing.

What I have done with the underwater metals on my last haul in 2014.
I first paint with zinc chromate primer all the running gear.
Then I coated - smeared a thin layer of a waterproof polyurethane over all except the shaft.
I used Loctite S30 polyurethane. It is smooth enough to cover with a thin layer.

Then bottom paint all of it.

My thinking is keep the water away from the metal and the chance for corrosion goes way down. I don't ever see any metal disintegration-pinking etc...

Another thing I wonder is, barnacles have bases they attach to metal. Those bases keep the metal dry away from salt water, so barnacle bases may actually help preserve the metal.

A prop edge, the barnacles get worn away, so prop edges can dezincify I suppose easier as they are exposed to the salt water..

So I am curious how the zincs are doing this time.
I think you are making a lot of mistakes here. First, don't put copper based bottom paint on metal running gear. A coat of polyurethane isn't going to protect it. If you want to paint your running gear, use paint designed for running gear.

Your anodes should not be "wasted" when you check them. There should still be 1/3 to 1/2 of the metal left when you replace them. Anodes are far cheaper than props and shafts.

Barnacles do not protect underwater metal.

You would do well to hire a professional boat diver to maintain your boat's hull and running gear. I can't tell you how often to have this done because it varies with the climate and conditions. Divers in your area will know how often it should be done and of course, you can ask slip neighbors or the marina manager. Just as a point of reference, in my area, it's every couple months in the winter and as often as every three weeks in the summer.

Your diver will inspect your anodes and replace them as necessary.

You might be able to reach the same speed with a fouled bottom as with a clean one but you will be using a lot more fuel to do so. I always make a call to have mine done immediately before leaving on a cruise.
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Old 02-03-2017, 12:31 PM   #8
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I would second everything WesK just posted. Anodes should be replaced when they are half depleted.

Regular cleaning by a diver will keep hard bottom paint lasting longer in my experience.
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Old 02-03-2017, 12:59 PM   #9
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The is no harm in putting copper bottom paint on bronze or stainless underwater gear. I have seen countless prop and rudders painted my whole life with no issues. My own included.

It's not the best way to paint them...but there is no harm.

But definitely not on aluminum.

Larsen Marine | Yacht Sales, Service, Storage | Waukegan, IL - Applying Bottom Paint

Applying
Antifouling paint should not be applied over a topside finish.
Propellers, outboards and outdrives are constructed of aluminum, stainless steel or bronze. There are no reaction problems in using paints containing cuprous oxide on stainless steel or bronze.
Care should be taken not to paint zinc anodes, which are often located next to the prop shafts, as this will seriously reduce their effectiveness.
When painting your outdrives, underwater metals and keels, the longevity of any antifouling is difficult to predict, as the coating adhesion is an issue, particularly on propellers, due to the harsh treatment these areas receive.


BoatZincs.com (978-841-9978) - FAQs


Answer T2: There are two dimensions to this topic.
First, the larger the surface area of an anode, the higher its electrical current capacity and galvanic holding voltage. For most boats, you want your anode surface area to be sufficient to maintain all underwater metals between -900 mV and -1100 mV relative to a silver/silver-chloride reference electrode.


Second, the longevity of a sacrificial anode is a function of its weight -- the greater the weight the longer its life.


Due to differences in water salinity, temperature, stray currents, and other external influences, you only know the right weight by actual trial. Periodically inspect your zincs, and when they have corroded to under 50% their original weight they should be replaced. To lengthen the replacement interval, increase the weight of zincs used.


If you have a steel or aluminum hull vessel that operates in salt water, use our Calculation Formula and/or give us a call. We've designed hundreds of corrosion protection solutions for metal boats and underwater metal structures such as docks, boat lifts, and retaining walls.
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Old 02-03-2017, 01:00 PM   #10
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Originally Posted by sdowney717 View Post
I know a planning hull a lot slower than semi or full.
I would think a full displacement which already moves more slowly, it won't have as much affect as a planing hull but still noticeable.

Anyone have observations they can share?

What % drop in speeds would you think for each type hull if hull is fouled but prop is clean?
What % increase in fuel usage?

My semi-displacement hull is somewhat fouled, I am onto my 3rd year, I splashed in fall 2014.
I have been thinking to haul spring 2018.
When the water warms up, I want to get under there and clean off as much as I can.

Thinking good gloves, a flat hull scraper like what you normally use when hauling out, mask and a hood to protect my head.
There is no nice way to say this, but make a vow today to stop neglecting your boat. Keep the hull clean and the anodes checked and replaced when needed. Check your shafts and props periodically. Yes, this may cost money, but it's the old "Fram-Pay me now or pay me later." It may cost you far more by not doing these things regularly.

If you're in Hampton, VA, your bottom is far more than "somewhat fouled" in that period of time. You're talking of scraping and the very fact it will need scraping says you should have done it sooner and more regularly and it would have been easier and less harmful. Get a diver to examine everything. Have you used a camera to even look under? Gopro's will do that for you.

How much do you use the boat? Do you know what kind of bottom paint you have on it?
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Old 02-03-2017, 01:13 PM   #11
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The bottom paint is some old stuff a friend gave me for free.
Yes, Hampton gets a lot of fouling.

At our marina, everyone I talk to has just painted the same paint on the running gear as the bottom.
And never have I heard doing that caused them trouble.
I just do what they did.

If you coat the metal with waterproofing, it will prevent it from corroding, if it stays dry.
I got no reason to doubt that.

Last summer we dove on the boat, the props had few barnacles, the hull a few.
But I have noticed now there are more now on the hull where I can see .

I can pop them off sitting on the swim platform pretty easy.

This boat is mostly for short day trips into the bay, like a picnic boat, not cruising.
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Old 02-03-2017, 01:23 PM   #12
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The reason shaft zincs fail prematurely is because the area where the clamping screws go is thin compared to the bulk of the zinc. If you paint around the area where the mounting screws go, it will inhibit the deterioration of the material in that area and they will last a lot longer before being flung off by the spinning shaft. This is what I do and it has lasted three years. Just installed (nothing else painted!):
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Old 02-03-2017, 01:31 PM   #13
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The prop is fouled as well and that will cause loss of push and extra fuel burn
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Old 02-03-2017, 01:44 PM   #14
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The reason shaft zincs fail prematurely is because the area where the clamping screws go is thin compared to the bulk of the zinc. If you paint around the area where the mounting screws go, it will inhibit the deterioration of the material in that area and they will last a lot longer before being flung off by the spinning shaft. This is what I do and it has lasted three years. Just installed (nothing else painted!):
Good idea, will do that.
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Old 02-03-2017, 01:50 PM   #15
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i know a planning hull a lot slower than semi or full.
I would think a full displacement which already moves more slowly, it won't have as much affect as a planing hull but still noticeable.

Anyone have observations they can share?

What % drop in speeds would you think for each type hull if hull is fouled but prop is clean?
What % increase in fuel usage?

My semi-displacement hull is somewhat fouled, i am onto my 3rd year, i splashed in fall 2014.
I have been thinking to haul spring 2018.
When the water warms up, i want to get under there and clean off as much as i can.

Thinking good gloves, a flat hull scraper like what you normally use when hauling out, mask and a hood to protect my head.
first is it legal to scrub your bottom in your state with what ever paint yo have on it? Secound there is no way to know what speed you will lose other than a direct comparrison of speed at a given rpm when it was clean and now when dirty takeing into account any weight changes in boat between the two speed trails. What can be said is that a dirty bottom does have an effect on top speed and efficency along the whole curve.
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Old 02-03-2017, 02:22 PM   #16
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first is it legal to scrub your bottom in your state with what ever paint yo have on it? .
Yes, it is.
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Old 02-03-2017, 02:37 PM   #17
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Yes, it is.
Yes, no problem with that in Va.
What we need is car washes designed for boats!
Drive the boat in and comes out clean other end.
This would make lot's of people happy, like environmentalist that hate bottom paint and boat owners that hate paying for it, and think of the fuel savings, less fuel burned means more money for you to spend elsewhere, plus less pollution into the air.

My idea is the entire process could be automated using 'AI' computers and underwater cleaning machines.

I have seen some automated hull cleaner videos on youtube.

http://www.searobotics.com/index.php...leaning-system

Of course new tech like this right now is expensive, with time that may change.
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Old 02-03-2017, 02:47 PM   #18
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first is it legal to scrub your bottom in your state with what ever paint yo have on it?
There is only one state in the country that has restrictions on what paints can or cannot be cleaned in the water. And it's the one you're in.
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Old 02-03-2017, 02:51 PM   #19
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On our current boat a foul bottom and or prop has reduced our fuel economy anywhere from 10 to 30 percent. So keeping the bottom clean actually pays for itself and biennial prop speed applications. It's one of those preventive maintenance items that yields more than it costs once you start using a certain amount of fuel. As they say your mileage may vary.
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Old 02-03-2017, 03:53 PM   #20
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Have not checked any anodes. I always have replaced them at haul outs, and typically my hauls are on a 4 year schedule.
Typically, the rudder anodes are there but wasted, and the shaft anodes loose or gone as in completely missing.
I don't ever see any metal disintegration-pinking etc...
You might think about changing your haul out schedule to every 3 years, or hire a diver to replace the zincs.

You probably won't notice any disintegration or pink color until you close a through hull and it snaps off in your hand. Hope your wooden plugs are handy.

I haul every year and each spring I replace anodes. I use fine grit sandpaper on all through hulls until I have shiny bronze. Slightest hint of pink, out they come. Last few years I have replaced one through hull and 2 raw water intake screens. Once I'm done, I empty a spray can of bottom paint up into the through hulls.
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