PROP Size?
 

Hello Newbe here, I just purchased a 1996 210 Shabah with 5.7mag. On the test run with new engine running great oil pressure 40 and the temp below 175 the GPS showed 45mph at a maximum trim allowed rpm of 4200. I was somewhat disappointed as everything about the boat said 50 to 57 mph. Out of the water we noticed that one off the three blades on the possibly original aluminium prop was bent in quite a bit.
The aluminium and the bend account for at least 5 mph we are at 3000foot above sea level here in Lubbock Texas.
The boat has a decent hole shot minimum 3 seconds to plan but the prop would not allow any noticeable trim gain. No major thrust as far as over all responsiveness. I want the punch and the top end - I am told the 4 or 5 blade prop is great for low end but not top end. Is there a perfect three plade pitch/dia for this boat? I do not want anything to take away from the top end and 50-55 would be great with a cruising speed of 30mph. Boat will be used to pull skis tubes. THANKS for any and all help.

What are the spec's on your current prop? How did you measure speed? GPS?

I currently run a 13.75 x 21p aluminum 3 blade and see similar performance. I'm thinking about an upgrade to a stainless 3 blade to see if top speed improves. My aluminum has a couple of dings in it...

4200 seems a bit on the low side for wot rpm. I'm usually at 4600 to 4800, depending on trim. You might want to confirm your tach is working correctly. There is a cylinder # switch on the back, it can get corroded and such, so switch it around a bit to clean it off and and verify that it's set to 8 cyl.

Top speed and watersports are a bit in competition with one another. A four blade lower pitch prop would probably be a better choice if watersports are your thing, whereas a 3 blade higher pitch would be the route if top end is your target.

Z202 has you on the right track. First off, you always want to keep your engine running within the recommended RPM range at WOT. So first, check to make sure your tach is set correctly as per Z202's instructions. Then tell us what size prop is on your boat now. Remember altitude definitely affects performance and can take 5mph or more off your top end. Now if everything checks out with your tach & you are only getting 4200rpms at WOT there is either a problem with the prop itself or you are over-propped and you need to get your rpm's up to between 4400-4800. If the prop is damaged then either get if repaired or replace it. You hinted that one blade was 'bent in'. That will definitely affect your performance. If the prop is okay & not damaged then you need to drop the pitch 2 - 3" to get the rpm's up within the range. If you are going to be spending a fair bit of time pulling tubers, wakeboarders etc then i would suggest going with a 4 blade SS prop. SS props perform better than aluminum props and the 4 blade gives more 'bite'. You might lose about 1 or maybe 2 mph off of your top speed.

You can also check out Mercury's prop selector tool. Click on the link below & enter the information it asks you for.
http://sites.mercurymarine.com/porta..._schema=PORTAL

As we've said in the numerous other threads regarding props, choosing the correct prop isn't an exact science....it takes a little educated guesswork and a little trial & error so if you can get any other potential problems (tach, damaged prop etc) out of the way it makes it much easier to figure out which prop will work best for your needs.

Where Do I Begin???
 

Hi Folks,I haven't been too active on the site however with all this talk about prop specs I need some advice. The performance of my SX2000LTD BR(1991) at the top end is just great. Its the coming out of the hole that really stinks.It takes a good 6-10 seconds to get the bow down at full throttle and then of course I have to power down to avoid ripping my wifes arms out of her sockets when she is water skiing!!!My marina has been playing with different props but does any one have any positive results they could share about this whole issue.It seems like its a hit and miss -try this one and that one but is there any science to the selection process???This season has not been the greatest weather wise so we have not been out as much as last year and as we all know a 5.7V8 is not the nicest on gas consumption...
Look forward to chatting
Mark Anderson
Lake Simcoe

I didn't buy my 5.7L for it's fuel economy... ;) :D

Anyhow, what props have you tried? A 4 blade prop might get you a better hole shot at the cost of some top end performance. If you know the all the tech details: WOT rpm, top speed, drive ratio etc. you can use Mercury's prop selector that mikeyt linked above.

Smart tabs are another possible option. There is a thread on them in the original Mariah boats forum.