Loss of speed, WOT RPM's ok

[bmac]

Took the boat out today for a ride to check on a continuing concern I've had for the past few weeks. It appears through the rpm range I'm running at a lower speed than I'm accustomed to. At 1800 rpm, I'm off by about 1.5 mph. At 2200 rpm I'm slower by about 2.5 mph and at WOT I'm slower by a whopping 5 mph. Both engines had normal, rated rpms at WOT. I also noticed that when I come off plane I feel a slight low frequency vibration, or shudder until I'm down to idle speed when all seems fine. Any ideas?

 

[Four Suns]

Bottom crapped up? (or running gear)

 

[bmac]

That was my original thought, but even with as warm as it's been most of it usually sloughs off with a little running this time of year. The boat did sit for two weeks in mid-July while I was in Punta Cana. I'm going to take dive when I get to Montauk on Friday, too late to do much this week.

 

[Bottom Line]

:smt001Brain....sounds like time to trade and get the 52DB.:smt001:smt001

 

[osd9]

The surface water temps in our areas have been exceptionally warm this year.....(btw...It's also keeping the bottom temps cold). I'd bet the two weeks in mid July, during the high heat spells we've been having, caused your props to get fouled with growth. It doesn't take much prop growth to loose a few knots.

 

[Alex F]

Brian,

I think that most people would agree that at this time of the year the #1 contributor is the bottom and undewater gear condition. Some marinas offer specials on mid season short haul outs to do a quick bottom wash. Becides the fact that your boat was sitting in the slip for 2 weeks the bigger question is how did you use her after that? If you took 15min cruise (at cruising speed) I don't think it's going to "shake off" all the growth. You need some good distance and you might still have something left on the bottom. As for vibration, if it's not barnacles, then there's always a chance that you have something wrapped on a prop or a shaft. As you said, a quick dive and you'll know what's going on there.

 

[bmac]

Thanks guys. I've scheduled a diver to come in on Wednesday to clean the bottom and running gear and to do an inspection. I'm hoping it's just marine growth causing this.

 

[bmac]

:smt001Brain....sounds like time to trade and get the 52DB.:smt001:smt001

That thought occurs to me frequently, but not as a result of this.

 

[bmac]

So Gary and then Alex win the prize for identifying the problem. I had the diver under the boat yesterday. While the bottom was clean my running gear was VERY fouled, mostly mussels and barnacles. My genny and a/c strainers were very nearly plugged as well. Hopefully, I'll notice a big difference on Friday when we leave for Montauk. Of course the 5,000 lbs of food, booze and gear that my wife loads on to the boat between now and then may negate any potential improvement.:smt101

 

[Alex F]

Good to hear that it's a simple fix, Brian. Were your shafts, scoop streiners, rudders and exhaust painted? I use Trilux 33 on all of my underwater gear. Props are the only items that I don't paint.

 

[Jack380AC]

Good to hear that it's a simple fix, Brian. Were your shafts, scoop strainers, rudders and exhaust painted? I use Trilux 33 on all of my underwater gear. Props are the only items that I don't paint.

I applied "Prop Speed" to the props last year. It is not cheap and must be done correctly (2 parts) but works fantastic. During a recent short haul, the bottom and all gear were totally trashed but the props were clean as a whistle. Good stuff and worth the expense.

http://www.propspeedusa.com/

[video=youtube;WHJKtoWmjpc]http://www.youtube.com/watch?v=WHJKtoWmjpc[/video]

 

[Alex F]

I agree on the propspeed. When I got my 420 the props had it on and they were very clean. Unfortunatelly, due to slight vibration on the port side I had to take it to the propshop to tune the props and as you can imagine all the propspeed coating had to come off. That's another problem one is facing when considering the investment. Luckily, I never had any growth on my props (and shafts for that matter) as I spin them often enough.

 

[bmac]

Good to hear that it's a simple fix, Brian. Were your shafts, scoop streiners, rudders and exhaust painted? I use Trilux 33 on all of my underwater gear. Props are the only items that I don't paint.

I'm hoping the problem is fixed, I won't know until I pull out to head to Montauk Friday (this traveling for work during the summer sucks). All of those items were painted, though my rudders, strainers and trim tabs were done with a spray, which I've always been a little suspect of. I think next year I'll insist that the only underwater gear that gets done with anti-fouling spray are my two transducers (which call for a spray application). My props are not painted either.

 

[Alex F]

... I think next year I'll insist that the only underwater gear that gets done with anti-fouling spray are my two transducers (which call for a spray application). ....

I just use masking tape to cover the lense of the ducers and paint them with the same Trilux 33 (for bronze) and plastic one (original SR installs) with Micron Extra. All roll on paints. I'm not sure how different those spray paints are, never used one.

 

[Robski97]

Guys ,
He's not kidding when he says 5,000 LBS of beer. There is no food there. Ive seen it first hand... BEER BEER AND MORE BEER.

Oh and if you took more then a 3 min ride across the bay this entire thread would be mute. Don't even get me started on slip hogging !!!!

Safe trip PAL. Maybe we come visit while ur slumming in my neck of the woods.


Rob