what prop size for a 86 searay 268 weekender?

[lime4x4]

Current prop is a 14.7 X 17 3 blade ss.The engine is a 5.7 liter mercruiser rated at 260 hp.The boat currently won't plane.We had it out this past sunday with 4 adults and 3 kids.between 2000 to 3000 rpms it will move at 3 to just under 5 mph. At wot it will do 13 mph but she won't plane.

 

[studlymandingo]

Re: what prop size for a 86 searay 268 weekender?

Do you have trim tabs?​

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

yes

 

[QC]

Re: what prop size for a 86 searay 268 weekender?

Mannnnn . . . we are getting a rash of these . . . 4800 RPM (your other thread) calculates to almost 31 MPH with a 2:1 ratio which you don't have . . . Probably closer to 1.5:1 which would mean even faster. I used a 20% slip . . . If your numbers are correct, you need over 66% slip . . . I ain't buying it. Something is broked. I trust Nova that it isn't planing, so something is fooked, orrrrrrr, your tach is 50% or more off.

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

i agree with something is "fooked" but i've been working on chevy's for almost 20 years now.And that engine at wot was running pretty close to 5000 rpm's.So it's either something is goofy with my sterndrive acka wrong ratio or something is slipping big time.How can i tell if a hub bearing spun?

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

well according to searay's website i should be using a 15.25X15 prop.Atleat that is what came from factory..

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

Ok buddy had a 4 blade 14.5X18 alum prop.That helped some.I can now go 10 mph at 3K.My wot came down some to 4700 with a top speed of 19 mph.The bow lifts and stays lifted.She still won't plane yet.And all the usual stuff was checked.As far as being stern heavy and water logged.So should i still go up in pitch yet?If So which one?

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

Well it seems my problems are do to the fact that it has the wrong ratio drive in it.My crank shaft spins twice to 1 prop turn which equals a 1.98:1 ratio. The drive is marked 1.50 R but when the drive was rebuilt by the previous owner they must've installed the wrong gears.So i'm going to order a new upper unit then restart the testing process all over again

 

[Silvertip]

Re: what prop size for a 86 searay 268 weekender?

To check for a spun hub, place a mark on the hub of the prop (near the nut). Place another mark directly in line with the first mark, but on the blade area of the hub. Now run the boat. I don't mean to be "cheeky" here but run the boat means run the crap out of it to stress the prop. When we assume things we often get a response like "well I didn't know you meant to actually drive the boat". Check the two marks. If they are still in line the prop is ok. If not, it's spun.

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

using a 15.25X15 3 blade alum prop i'm able to get the boat to plane. She comes onto plane at 3800 rpm's but it take about 45 seconds to get there.My wot is now at 4000 4100. I basically have to have the boat at wot to keep her on plane.Any ideas on what type/size prop to try next?

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

ok took the boat out tonight. The 14.25X17 3 blade ss prop gives me a max speed of 18 mph with a decent hole shot but boat doesn't plane 3500 wot.The 15.25X15 3 blade alum prop when properly trimed out gives me a max speed of 32 mph and the boat fully planes at around 26 mph 4100 wot but it takes over a minute to get the boat to fully plane. The 16x13 maxes out at 19 mph at 4500 wot and boat doesn't plane at all

 

[lime4x4]

Re: what prop size for a 86 searay 268 weekender?

ok we took the boat out tonight again..I just love burning gas...lol Anyway i tried the 16X13 prop. Full throttle trim tabs up. Maxed out at 18 mph 4300 rpm. When i maxed out i started to put the trim tabs down. the boat started to pick up speed and planed. Maxed out at 35 mph 4500 rpm's. Then i tried the 17 ss prop that came with the boat. Samething full throttle maxed out at 18 mph 3500 rpm's. Started to put the trim tabs down the boat picked up speed and planed. max speed 36 mph 4600 rpm's. Put the 15 back on. Maxed out at 18 mph 4000 rpm's. put the trim tabs down she picked up speed maxed out at 35 mph 4200 rpm's. I'm at a lose here..lol