Losing 30% of top speed, same RPM, why?
 

Hi guys, ive run out of places to ask, so here is my last shot. Sorry its not a performance boat, but like i said...i have no idea whats going on here. My girlfriend has a 210 searay bowrider, with a 5.0 EFI, alpha drive, and its bone stock from the factory. Early last year it ran a consistent 45 mph on the speedo i had not driven it. (according to boat test it should run about 49). motor says optimal RMP range is 4400-4800 on the arrestor. Ok, so im driving this thing and it feels like we are pulling an anchor! its running 32 mph @ 3900 rpm's (i verified on my phone GPS) and then i start trimming it up bit by bit...it hits 34, then dips to 32 back up to 34, down to 32 again, i did this over and over, and then i hit about 4800 RPM and we are struggling to hold 30 MPH...any ideas here? boat sits a bit, and might have slight algae on the bottom, but i cant see that accounting for 12-15 mph. nothing changes year to year, same prop, body of water, etc...im gonna pull it out this week and have a look, any idea what i should look for or do? Boat gets out of the hole fine, and planes out fine, its just painfully inefficient running WOT.

If it matters i have a 232 baja, and fully trimmed out its a handful, this thing trimmed out feels like the tabs are all the way down, only problem is, boat doesnt have tabs.
thanks everyone!

A dirty slimey bottom can kill your speed. I'd guess you have spun a hub but you say it get out of the hole Okay. Rope around the Prop??? Broken Prop????

All of the above plus coupler?

Since you are running on the Chain O Lakes, I would check your prop and also pull the boat and spray the hull with a mix of Sno-Bol and water to kill the slime growth. 2 weeks in the water and you will have fuzz growing on the hull that will rob you of at least 5 mph.

Try fresh fuel, you'd be surprised

Could be a hundred things but given that your presumably turning the same RPMs as always the most obvious culprits are likely crud on the hull bottom, a failing coupler or prop hub, or a banged up prop.

thanks guys, ive been able to check the prop edges while in the water at the sandbar, and they all seem ok, much better than the prop on my boat. i know there wasnt anything in or around the prop or drive as well. Guess i should pull the prop off and check the hub and go from there...im thinking a failing coupler would cause me to run 5 mph and not 30. Ill also give the bottom a scrub this weekend and see what happens.

Check the emergency brake.

Pull it and power wash the bottom.

does the boat have tabs? are they all the way up?