Speed Loss with Dirty Boat Bottom

[dzurinko]

I own a 2001 Key West Bay Reef 196 with a 130hp Honda. I keep it in a freshwater lake in Florida at a boat slip. Water temps are consistently around 90 degrees. Its been in the water about 5 months. About one month ago, I took it out for a spin and did some fishing. At 5300 rpms, I was clocking about 32-33 mph. Seemed to run great. I brought it back and parked it. I didn't use it for a month. Then last week, I took it out for a 3 hour run through the chain of lakes. But I immediately noticed when I left the marina, I could only get about 21 mph out of it. Engine still ran great, but speed was an issue. Thought I had a bunch of weeds around the prop but I stopped and checked and that was not the case. The RPM's were still normal at about 5300. From talking to other people, I initially was convinced I had a spun prop although that seemed a bit weird because the last time I parked it a month before, it was running at 32 mph. . So today I pulled it out of the water to take the boat to a repair facility for some other work I needed done (Install a new Garmin Chart plotter and a new seat) and thought I'd have them look at a possible spun prop. But what I noticed as soon as I got it on the trailer, was a layer of green scum from the water line and completely covering the bottom. So my question is can I actually lose 30% (32 mph down to 21 mph) from this green algae? I would never guess that big of a loss from a dirty bottom. Its in freshwater and of course no barnacles or anything like that. Just green slime. Is a 30% loss of speed possible or does anything think a spun prop is more of a possibility?

 

[Scott Danforth]

professional swimmers shave their legs, back, and chest to reduce drag from the little bit of body hair.

depends on how thick and scraggly the algae growth is.

 

[dzurinko]

Thanks Scott for getting back to me. Its certainly not as thick as a carpet but I know it must have SOME impact. You can scrape it off with a fingernail. But when I bought it and initially put it in 5 months ago, I had the bottom waxed and buffed so I was shocked to see it completely green/brown in such a short period of time. I'm sure a good power wash will get it off. But the lesson for me here is don't wait 5 months to pull the boat for routine cleaning/maintenance. I just have a hard time comprehending a 30% loss in speed from some green lake scum....IF that's what's causing the speed loss.

 

[H20Rat]

There is no way you would drop that much speed and only drop 100 rpm. How about buildup on the prop itself?

 

[dzurinko]

Nothing on the prop smokingcrater. Just the bottom of the boat.

 

[jimmbo]

I'm surprised it took 5 months to cause issues. The longest we were able to leave ours boats in was two weeks before they needed the hull scrubbed. If the lake ever got above 65, we considered it boiling. Pressure washer and Scotchbrite pads will remove the Braking Lining off the hull. You might want to paint the hull below the waterline with a paint that discourages vegetation growth

 

[dzurinko]

Thanks Jimmbo. I always assumed that freshwater did not require bottom painting, but I guess I was wrong. So do you think the 11 mph loss is from the green scum on the bottom and NOT a spun prop? It even takes 10 seconds to get up on plane where I used to be up in 4-5 seconds.

 

[gm280]

Thanks Jimmbo. I always assumed that freshwater did not require bottom painting, but I guess I was wrong. So do you think the 11 mph loss is from the green scum on the bottom and NOT a spun prop? It even takes 10 seconds to get up on plane where I used to be up in 4-5 seconds.

I certainly wouldn't be a bit surprised to see such a drop in top speed. Think about all the drag the slim is creating. Water drag is cumulative,and anything that creates such drag is going to effect the speed quickly.

I remember I had a Bass Boat the topped out at about 52 MPH, and then I installed a jack plate and moved the engine up some. I ended up at 63 MPH. Now I can't accredit it all to just the reduced drag from the lower engine. But a lot of it was. So I do think you will recover you top speed if you clean the hull well.

And I know I will get chastised (again) for saying this, but when I would wax that entire Bass Boat, I would see an increase of about 2 to 3 MPH top end speed as well. But it didn't last but a couple outings before it diminished again. And while others say that can't be true, I will say it was, and not only once, but every time I waxed the hull. JMHO!

 

[wahlejim]

Keep in mind that you probably cleared a lot of the thick stuff when you were going 21mph and what is left over is just the base layer. 3 weeks in those temps is more than enough time to make that difference.