Looking for advice on 21p aluminum prop
 

I have a 2000 Mariah Shabah with the 4.3 carbed mercruiser 190hp. I am looking to move from a 19p to a 21p prop for more top end. What brand is recommended? What diameter are others running? I see everywhere from 13 3/4 up to 14 1/2. I do not want a 4 blade. Anyone have a recommendation? I hate to just buy one and hope it works for my needs.

Re: Looking for advice on 21p aluminum prop
 

I'm sure you already know this but i'll repeat it anyway. Moving up to a 21" prop will cause you to lose your low end acceleration & hole shot. That said: if its a 21" you want then 14.25 x 21 is the standard size. It wont hurt to be a 1/4" larger in diameter. In aluminum i would suggest a Michigan Wheel Vortex or a Quiksilver Black Diamond. Both are good general purpose props. If you are feeling a little flush & want SS then i would suggest a Stiletto Advantage.

Re: Looking for advice on 21p aluminum prop
 

Thanks Mikey. I understand I may lose some bite, but I think the type of boating I do may be more suited to the higher pitch prop for speed and efficiency. Typically my wife and I boat together, sometimes with another couple, but many times just the two of us. We are not usually skiing or pulling water toys. Mostly we cruise about 30 miles down a river in Massachusetts into the Mount Hope Bay in Rhode Island and hang out in Newport for lunch or shopping. I do have smart tabs and a well tuned engine. I need a spare prop anyway and was thinking we could swap the 19 and 21 depending on the load for that day. I think you told me a while back that you have both sizes. Is the 21 too high for this set up? I like the higher top end for a quick rip once and a while. I really appreciate your advice. Thanks!

Re: Looking for advice on 21p aluminum prop
 

Nah, the 21" will work just fine for mid range cruising but just dont expect much in the way of low end grunt or acceleration. I have a 20" 4 blade & a 21" 3 blade and if i'm going for a distance cruise i will throw on the 21".

Re: Looking for advice on 21p aluminum prop
 

We have a 1995 Mariah Barchetta 182 with a 4.3L mercruiser and we operate a 21Pp SS prop. For us it seems to have plenty of low end grunt because we do a good deal of wakeboarding and even with 3 guys in the boat and a 195 lbs guy on the wakeboard, our set-up still gets out of the hole just fine.

We also tend to have the max number of passengers on board more often than not because we are the first of our group of friends to have a boat. And I am happy to report that as long as one person sits up front (which one has to anyway), there are no issues with even 6 people in the boat.

I do find it a little odd that we get such great results, but it must be repeatable because it performs well all the time.

So, I imagine the 21p prop would also work well for you, especially since you have smart tabs.
.

Re: Looking for advice on 21p aluminum prop
 

Hard to compare directly as you have a different year, a different model and different weight which all add in to the effect on a boats performance. Glad to hear your Barchetta performs well with the 21". There is someone else here (my senility is kicking in & i can't remember who it was) that runs a 23" prop on their 94 Barchetta 180 and is very happy with how it performs. My '96 Shabah 180 didn't do well with the 21" at wakeboarding etc until i installed Smart Tabs and the 20" - 4 blade prop but it did cruise nicely. Bbrophy's 20' boat will weigh more that ours & is using the same motor so it will work just a little harder than ours at getting onto plane. The Smart tabs will definitely help and having a choice of props available is always a good idea.

Re: Looking for advice on 21p aluminum prop
 

I really appreciate all of the input you guys have provided. Just to clarify, my boat is a year 2000 Shabah 182, I think the same hull as MikeyT. I may have added some confusion by saying it was a 2000. Not sure if the year makes much difference. I run a 19p aluminum prop with smart tabs and get great hole shot and about 47mph top end and 4900 rpm. I think the smart tabs I added may have slowed me down a couple of ticks, but are great overall and my best upgrade to date. I have tried most of the smart tab settings and use the second lowest for every day cruisiing and the middle setting for the few times we go skiing. It is probably just my male ego, but the 50mph club would be fun and a planing at a lower rpm for my weekly 30 mile run down the river would also be a bonus. This morning I am tucking my boat into a garage for the winter and will wait anxiously for spring. Based on all that you guys have said, I will grab myself a 21p prop over the winter. I will stay with aluminum as a precaution. Already lost my original prop to a pesky rock! Oh, here is a picture of my little guy docked in Newport RI for an afternoon lunch. In the words made famous in the movie "Jaws" ......"I think we need a bigger boat" Might have to look at that 302 for sale. Thanks everyone.

Re: Looking for advice on 21p aluminum prop
 

Hi, I have a 2006 SC23 with 230hp carb motor the prop that came with the boat (I'm second owner) was an 20 inch 4 blade aluminium which has been damaged . The boat always cruised well but took a long time to get to plane especially with more than 2 people on board.

As I have no starting point other than the 4 x 20in can some one help me with info as to the best all rounder to go for , SS is ok but the 3 vers's 4 blade and pitch size has me scratching my head.

Thanks
Will

Re: Looking for advice on 21p aluminum prop
 

Was the prop damaged when you bought the boat? That would likely explain the planing difficulties. With your boat a 19" or 20" would be about the right pitch. To give an accurate assessment though we really need to know what your rpms were at WOT. You can always visit the Mercury Prop Selector site and plug in your information to get an accurate starting point.

Basically, lower pitch results in higher rpms and better holeshot but reduced top speed. Higher pitch reverses each of those results. 4 blade props tend to provide better acceleration & smoother cruising but usually at the cost of a little off the top end. Your engine (5.7?) has an RPM operating range of 4400 - 4800. Ideally, your WOT rpms should be very close to 4800 but as long as you stay within that range your motor is running efficiently.

Re: Looking for advice on 20 p aluminum prop
 

Gday Mickyt,
Thanks heaps for getting back to me .

My motor is a 5.1 Lt 230 hp.
No the prop was not damaged it was new when we got the boat , we hit a submerged rock up the river on Friday ( we weren't going very quick so only prop bought it) .
The previous owner placed the 20 inch alu prop a week before we purchased the boat he had not even tried it out.
Hence my problem with no starting point cannot find out what prop was on the boat originally .

The WOT is about 4200 rpm with the 20 inch prop and 40 mph, by my reckoning this is down on what it should be ...but not knowing what is factory .

I have gone to the Merc site and have placed all possible WOTS and mph's to 46 mph to see what is recommended again just started to get more confused.

Big problem out here is there are so many so called experts on out boards with none installing me with confidence about inboard/stern drives .
Thanks again.
Will

Re: Looking for advice on 21p aluminum prop
 

If you are at 4200 rpms at WOT then yes, you are a little low. A 1" drop in pitch to a 19" 4 blade will add about 250-300rpms at WOT. Going to a 3 blade 19" will add 300-325rpm but you will lose just a little 'bite' when going from a 4blade to a 3blade. Going from aluminum to SS will also give you a slight performance improvement but at a higher price point.

Unfortunately there is no such thing as a correct 'factory' prop for most applications. Two similar sized boats can use markedly different props. For example one of our members has a 18' Barchetta while i have a 18' Shabah. I use a 20" 4 blade most of the time. The Barchetta runs a 23" - 3 blade and gets good performance. I've tried a 21" on mine & it wouldn't pull a skiier out of the hole. Its not always easy to get it right. Selecting the correct prop is sometimes a matter of getting an idea where to start & then trying out 2 or 3 different ones. A lot of prop shops will have trial props that you can borrow (or rent) and see how things work. At this point though & based on what you have stated, i suspect a 19" 3 or 4 blade will improve things for you.

Re: Looking for advice on 21p aluminum prop
 

Going up in pitch from 17 to 21 will loose approx 400 to 600 rpm. You want to make sure you stay within the WOT recommended RPM range to prevent lugging down the motor. You may not gain much top end going to that higher pitch due to the lower torque of the V6. A 19 pitch may be a better starting point. Prop selection is a tail and error process.

Good Luck

Re: Still can't test my new prop
 

So...the weather here in Masachusetts has been nothing short of awful, raining and cold every day so farthis spring. It literally has not gotten higher than the 60's yet and has rained EVER DAY in May. I am dying to try out my turning point propeller and will report as soon as I can get my boat out. It is waxed, the battery charged and the motor has been run on muffs...so all I need is the weather! Stay tuned.

Re: Looking for advice on 21p aluminum prop
 

I had the 14 1/4 by 21 on my 5.7 92 Shabah don't waist your time or money, if you tube or ski the loss on the low end puts such a strain on the motor when you increase the pitch and you will gain maybe 2 mph on the top end. I tried 5 or 6 different props aluminum, different size and pitch 3 blade high performance even a $500 stainless prop and got 3 more mph at top end and it took half the lake to get that speed. By dropping down the pitch i was able to pull three tube six people, my poor Mariah and lost 4 mph at top end. You can call Merc Cruiser give them the engine serial # drive serial# and model of the boat they will recommend different sizes. Sorry for the long lesson on props but i worked on this exact issue for five years before I just stayed with the stock size prop. Happy boating don't blow it up!!!

Re: Looking for advice on 21p aluminum prop
 

What "long lesson on props"? You gave your particular experience with your particular boat and engine. It doesn't apply to all boat/engine/outdrive combinations.

Re: Looking for advice on 21p aluminum prop ..RESULTS
 

So I finally got my boat out today and has a chance to test that 21 pitch Turning Point aluminum propeller I bought. My hope was to improve the top end a few miles per hour to 50. I was running a standard aluminum 19 pitch and getting 4800 rpms and 47-48 mph top end. Well I am very disappointed. My best top speed on gps was 46.6 and the rpms maxed at 4400. The hole shot is a bit slower but still pretty good. The prop sounds louder due to the venting I guess. This prop ventilates ( or is it cavitating?) and slips a lot on turns and on takeoff. Overall I hate everything about it. Had I gotten the extra top end speed I still would not be happy due to the other charactaristics. So it looks like the stock 19 was a better fit. I would guess my best bet for maximum speed would be a 19 stainless. As for Turning Point props....don't waste your money. Mine is now my emergency spare.

Re: Looking for advice on 21p aluminum prop
 

Personally i would probably unload the Turning Point on some unsuspecting Bayliner owner, buy a 19" cupped SS prop such as a Stiletto Advantage and keep the aluminum 19" as a spare.

Re: Looking for advice on 21p aluminum prop
 

Mikey I could not agree with you more. I will post my almost new Turning Point prop on the Bayliner web site and praise it's high performance characteristics. I have to admit, Mariah knows best on prop size and pitch. I would recommend to most people, now that I have some real experience, to just move to stainless as a performance boost. Don't mess with pitch if your rpms are right in the first place. I am not sure why I expected my boat to be able to push those extra 2 inches of pitch at the same 4800 rpms. Thanks to all for their input.