Boat speed decreased by 1 knot

Benny17441 · Oct 19, 2016

Check the cutlass bearing and perhaps the accuracy of the instruments and method used to measure speed.

Ralph Johnstone · Oct 19, 2016

mytime said:
Do you think that would slow the boat down 1 Knot?

You'd have to compare your boat speed to the same original tach speed to make a comparison.

Scott T-Bird · Oct 20, 2016

I'd guess that you had a layer of algae on the bottom that can slow the speed down substantially. I've always needed to scrub the bottom periodically in the summer to get that knot back. Your water may be too fresh to affect the zinc much. Also, if stray current isn't present where you keep your boat, you should see longer life. That's an impressive colony of barnacles! They are aren't improving your boat speed. I am curious how you plan to get them off and deal with that. I have a similarly impressive colony (and my zinc shows little deterioration, as well).

capta · Oct 20, 2016

When water cannot flow through a cutlass bearing, which is water lubricated, it can bind up and even weld itself to the shaft, causing it to spin in the strut, though I doubt this would cause a 1 knot decrease in speed. A build up of barnacles on the shaft would interrupt the even flow of water across the prop which can also contribute to your speed decrease a bit.
As above there are so many other factors in the equipment that measures boat speed, I'd look there for at least some of the problem.

Gunni · Oct 20, 2016

Up Middle River way you should be using an aluminum anode. What little sacrifice your forward shaft anode experienced was salted over and the anode insulated - made ineffective.

heritage · Oct 20, 2016

I notice you have two prop zincs that show very little wear. That reminded of how I cured a fast growing barnacle buildup on the ss prop shaft and bronze propeller. A guy told me to try removing the prop zinc and see what happens. No more barnacles and NO my prop and propeller did not turn into swiss cheese. Seems that the galvanic action between the bronze and stainless keeps the barnacles at bay. Not suggesting you try this,,, just food for thought.

Steve Dion · Oct 20, 2016

Looks like you should have lost more speed than 1kt.

Our HV'36 lived in fresh water and the "zinc" lasted for 10 years. The screws finally corroded through.

Scott T-Bird · Oct 20, 2016

No, freshwater actually takes magnesium. Aluminum is for brackish. If anything, try removing one. I don't know why they would install 2 anyway. It is probably overkill and it doesn't help your speed either. I suppose the electrical activity helps make the barnacles uncomfortable if you don't use a zinc. It would be risky in my opinion.

fstbttms · Oct 21, 2016

Steve Dion said:
Our HV'36 lived in fresh water and the "zinc" lasted for 10 years.

That's because it wasn't doing anything, including protecting your running gear.

Gunni · Oct 21, 2016

Scott T-Bird said:
I don't know why they would install 2 anyway. It is probably overkill and it doesn't help your speed either.

It is common to double zinc in the Bay where many boats stay in year round. Gives plenty of anode, and if he had the right anode he would need it to make a year.

Chief RA · Oct 21, 2016

Some of these anode comments are an indicator of the belief that only about 20% of sailboat owners are competent sailors. The rest of them merely OWN a sailboat! Chief

fstbttms · Oct 21, 2016

Scott T-Bird said:
I don't know why they would install 2 anyway.

Because two anodes provide protection for twice as long as one, that's why.

Scott T-Bird said:
...and it doesn't help your speed either.

A Catalina 30 with a barnacle garden growing on it and you think an additional anode is the problem?

Chief RA · Oct 21, 2016

The current still travels through the shaft. By having 2 anodes it would split the current passing through the anodes to or from the water equally; thus substantuating Gunni and fstbttms posts. Approximately (shaft length between anodes plus bonding) 1/2 the current through each one=twice the life of both of them! Chief

Scott T-Bird · Oct 21, 2016

No, I think algae growth on the bottom is the likely problem because it always has been for me. After I scrub off the slime about 3 or 4 times per season (I usually try to get at it in late September for the last time), I always gain back at least 1/2 knot. I'm sure the barnacle garden doesn't help, but I'll admit I don't know much about zincs. I never used a zinc or magnesium anode in fresh water and I never found any corrosion either, so I'm not even sure why anything is needed for fresh water.

As for the two zincs, I'm guessing that most people in the northern Chese store their boat on land in the winter. That provides anybody with ample opportunity to replace a diminished zinc in plenty of time. It also appears that there isn't anything unusual going on with regard to stray current, which could use up the zinc, I only suggest he remove one. He obviously doesn't have a problem with his zinc disappearing and it doesn't look like he has any corrosion going on (maybe the freshwater has something to do with that), so why not take one off? If he leaves the boat in the water year round, then fine, leave 2 zincs on, but it looks like he already pulled it out.

Chief RA · Oct 21, 2016

If you only have slime on the ablative paint I would not think it would slow you much. The other point on cleaning it off is you just removed some of your ablative paint as well. Unless your racing I'd leave it, and I do. My boat presently has 3 seasons use on it with the same bottom paint and when I pull it out next month I will access it then. I expect to only clean the small amount of long grass up on the waterline and just rinse the bottom. Chief

Warren Milberg · Oct 21, 2016

Think you have barnacles? Think again.... Do you think this would slow me down?

Scott T-Bird · Oct 21, 2016

Chief RA said:
If you only have slime on the ablative paint I would not think it would slow you much. The other point on cleaning it off is you just removed some of your ablative paint as well. Unless your racing I'd leave it, and I do. My boat presently has 3 seasons use on it with the same bottom paint and when I pull it out next month I will access it then. I expect to only clean the small amount of long grass up on the waterline and just rinse the bottom. Chief

You'd be surprised, but the only way I can tell is by the speed I obtain when motoring at a specific RPM. Otherwise, when sailing, the conditions are too variable to be able to tell. As for losing the ablative paint, I'll soon find out sometime in November. I've never had an ablative paint on the boat before this season, so I'm on a learning curve. Either way, I'll still scrub the bottom. I don't want it to look like Warren's!

The other thing I have noticed is that I don't obtain the speed while motoring that I did in fresh water. I'm guessing that the density of the water has something to do with that ... or maybe I gained weight in the past year.

fstbttms · Oct 21, 2016

Chief RA said:
If you only have slime on the ablative paint I would not think it would slow you much. The other point on cleaning it off is you just removed some of your ablative paint as well. Unless your racing I'd leave it, and I do. My boat presently has 3 seasons use on it with the same bottom paint and when I pull it out next month I will access it then. I expect to only clean the small amount of long grass up on the waterline and just rinse the bottom. Chief

So you are advocating for never cleaning your hull? Oh brother.

All of these boats are cleaned on a regular basis:

I cleaned this Max Prop two months ago. Here is what it looked like yesterday: