Prop for an SX20

[coooeee]

My 2006 Mariah SX 20 has the 21" Black Max prop via a 220 hp 4.3l Mercruiser Alpha 1. At present in a light boat I get 55mph at 4800RPM but want to increase performance for wake boarding/skiing. A marine dealer suggested the Mercury HI 5 at 21", any suggestions would be appreciated. P.S top speed is not a major consideration.

Thanks

 

[180shabah]

Re: Prop for an SX20

Welcome to Iboats coooeee.

You need to ask this question in the Prop forum, a little higher up the list. There are some very knowledgable over there. Repost exactly what you have above and they will help you find a good prop for your boat.

 

[SpinnerBait_Nut]

Re: Prop for an SX20

I will move it there now.
Welcome to iboats.

 

[coooeee]

Re: Prop for an SX20

Perhaps I asked the wrong question..any one...Beuler..?

 

[tmh]

Re: Prop for an SX20

I wonder if you're almost 'between sizes" on the Hi 5? Seems if you put a 21" 5-blade on there you may wind up too low on WOT RPM but a 19" may put you over. Maybe it depends on "normal" load on the boat as compared to how it was loaded when you tested it.

I'm not sure you'll be able to find the answer without testing several options. Maybe a 20" 4-blade SS would be just right? Should give you better low-end and middle range power for water sports. May keep your rpm pretty close to where you are now.

I'm certainly no expert, btw, just throwing out some ideas to help the thread along! Good luck getting it set up just right!

 

[180shabah]

Re: Prop for an SX20

Bump

 

[coooeee]

Re: Prop for an SX20

Thanks for the reply and the bump, you guys are friendly here. There are not many experts (english speaking) in my location, so testing a range of props is difficult. I will eventually buy one on line and have it shipped based on what I learn for myself. I had a service done recently and the Merc guy hooked up his laptop, as I looked over his shoulder I noticed that the engine is running around 2800 RPM for most of its hours. I usually wake board at 18-20mph so I assume that would correspond with the 2800rpm ?? Is this RPM a bit low and if so then a 19" High 5 would be better than a 21"??. My boating knowledge is limited to the 4 months I have had the boat so any help is welcome. I mention the High 5 purely because it was suggested by a marine store in London following an email enquiry.

Coooeee!

 

[tmh]

Re: Prop for an SX20

C'mon guys, help this fella out. Someone has to have a more specific answer for him!

Here's my take....it depends on the "normal" load in the boat. IF the rpm/speed specs you gave are for normal load, then you may be OK with a 21" hi 5. IF they are with a lighter than normal load, then I'd say either a 19" hi 5 or 20" SS 4-Blade would do the trick. For water sports most say error on the lower pitch side as it gets you better low-end performance.

Me personally, I'd be too cheap to buy the Hi 5 as it is very expensive. Easy for the prop dealer to recommend one, as it WILL likely perform well for you, and HE'S not paying for it...but is it the only upgrade you can get?....no way. You can get a 4-blade SS at a reasonable cost on eBay. I'd bet that would be a big improvement for hole shot and mid-range for you.

 

[180shabah]

Re: Prop for an SX20

There are not many experts (english speaking) in my location...

Didn't you guys just build the "Whole World" over there. There should be plenty of english spoken in the "North American" neighborhood

 

[coooeee]

Re: Prop for an SX20

Thanks TMH, what you say makes sense to me, and you are correct about the price. I am not doing any competition stuff, just me and the kids so a cheaper option would suffice. The figures I quoted were in a light boat, myself and a 10 yr old so a lower pitch for normal loads would be a good idea.

"The World" is still under construction and boats are not allowed near it, but when its finished I'll pop over and visit you with my new prop...!

Coooeee!

 

[180shabah]

Re: Prop for an SX20

I find that whole project simply amazing. I would love to go see it, but I guess I will have to make do with pictures for now.