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| Prop for 180 with 3.0 Mercruiser https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=1051 |
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| Author: | Rob [ Sat Jun 30, 2007 2:45 pm ] |
| Post subject: | Prop for 180 with 3.0 Mercruiser |
So the stock Prop is a 14.5" X 19" Pitch Prop and I can't figure out if I should go with a 14.5" X 18" 4 blade or 14" X 20" 4 blade (All Aluminum) Any one out there able to let me know what 4 blade props you went with and how performance was/is? (RPM, Hole shot, holding, etc...) Thanks! 
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| Author: | mkperceptions [ Tue Jul 03, 2007 12:20 am ] |
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I was told to use the 4 blade with the same pitch and diameter and it would make a big difference. I am not sure I would go any larger or smaller I think the stock prop is pretty close to where it should be so go for a 4 blade and I think things will be good. |
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| Author: | Jim_R [ Tue Jul 03, 2007 10:09 am ] |
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I'm of the opinion that it's always best to do a try before you buy with props, even if it costs more locally than over the 'net. A quick prop change and some carefully timed runs where time to plane, planing speed, and top speed are documented and compared for a couple different prop styles and/or pitches will ensure you find the prop with the characteristics you are looking for. Anything else is a shot in the dark. Don't forget to do the runs with the stock prop first! Hmm... maybe there's an idea for a new business line for marinas here, prop rentals - you break it you buy it. 
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| Author: | mkperceptions [ Thu Jul 05, 2007 6:32 pm ] |
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Here in california there are no try before you buy shops. I wanted a new prop and asked the shop that I bought the boat from and they laughed and said not here in california you wont find a shop that does that especially not in the bay area. I said "well what if i dont like it" and they said "sell it on ebay" blah I want to try a prop intead of blowin a ton of money on props i dont want. |
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| Author: | Rob [ Mon Jul 09, 2007 6:10 pm ] |
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Same here. No Test drives if you will. I have the 2 choices. One for hole shot and the other for better overall performance. After tubing and skiing this past week, not sure if I need the 4 blade. Hole shot seems fine with me being towed behind the boat (220 lbs) on skis and 2 of use (both about 220 lbs) on tubes. I give up... 
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| Author: | thompsbren [ Sun Jan 27, 2008 5:14 pm ] |
| Post subject: | Re: Prop for 180 with 3.0 Mercruiser |
I know its been a while, but I was wondering if you ended up swapping out the stock prop and if so, what the results were. I've got the 3.0 in my 180 and find that I've got a lot of throttle left at 4600rpm. I usually just cruise with light loads, so I'm considering something with a little more pitch. |
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| Author: | Walt [ Sun Jan 27, 2008 5:51 pm ] |
| Post subject: | Re: Prop for 180 with 3.0 Mercruiser |
Hopefully this will help many with prop decisions. I have been using this link for a few years with great benefit.... http://www.go-fast.com/Prop_Slip_Calculator.htm First, Plug in your Gear Ratio (should be stamped on your outdrive). Next, the prop pitch you have BEEN using (if it's stainless, add about .5). If you have the Full Throttle RPM that you have been achieving with this prop, plug it in the RPM column. Click the button to calculate your thoeretical speed. Next, enter the actual speed you have achieved with THAT PROP, at the RPM you entered earlier. Click the appropriate button to get your slip. Your slip is relatively constant for your Hull once your boat is planed out. From about 30 mph on up, this should stay about the same no matter what prop/speed/RPM you use. Therefore, remember it and keep this slip value handy. Once all the other variables have been entered, and slip calculated, it will allow you to pick the best prop for the Top Speed, and WOT RPM you are trying to achieve. For most of us, slip will be in the 8-13% range. If you have something negative, or grossly out of that range, try going out and verifying your RPM, Speed, and Gear Ratio. Now, with the calculator, just try plugging in different prop sizes and RPM ranges to get the results you are after. The best way I found was to work backwards..... Knowing all the variables, desired top end speed, and WOT RPM, leave the pitch blank and see what you get. Again, prop pitch works well uncorrected for Alum props. For SS, or 4 bladed Alum, add .5 to your actual prop pitch. I've used this on a few boats, Alum, SS, and 4 blade Alum props without trouble. The best results will be achieved with the most data, and the most accurate data (ie, GPS vs Speedo.... just split the diff). Try it a few times at diffent speed/RPMs, and recalculate. Write down your data so you are not guessing later. This will save some bucks and headaches propping your boat, especially those guys with way too underpowered. As far as purchasing a prop, most shops will match the best deal you can find. I have found iBoats.com has very good prices, and a very good set-up for locating the props that are right for you. Last time I bought a prop, I just found the matching one on iboats, printed it out, and took it to the store. They matched the price, and took my trade without any flak. Oh yeah... and if switching from 3 to 4 blade... keep in mind, you'll need to adjust your trim tab... if you don't have one, may need to get one. My old 1800 Maxum went thru about 3 props, until I settled on a 4/20 Alum. When I switched to 3/21 SS, I found the trim tab wasn't needed. My 210SS doesn't even have a trim tab, as I'm sure many of yours do not as well. So, I probably won't go to the 4 blade, but will experiment a little with the other 3 bladed props I have. Good luck, the season is getting closer! |
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| Author: | robbo3 [ Tue Feb 12, 2008 9:48 pm ] |
| Post subject: | Re: Prop for 180 with 3.0 Mercruiser |
Walt - are you saying that going to the stainless prop worked better than the 4 blade? If so, what were the major differences between the two? I use the 4 blade 14x20 on my 4.3 Volvo SX drive (Merc prop with Volvo hub). It works out great for curing slow speed wandering and running on plane at slower speeds, but I have a significant drop (about 7mph) in top end speed when compared with my 3 blade prop. I'll throw the 3 blade on when the speed limits are not in effect early and late in the year and use the 4 blade throughout the summer for watersports. I also recommend testing if the option is available. We went throug a shop that let us buy the prop and take it out for the day. If we didn't like it, we could get a full refund if we didn't damage the prop. |
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| Author: | Walt [ Fri Feb 15, 2008 9:15 am ] |
| Post subject: | Re: Prop for 180 with 3.0 Mercruiser |
Yes. I'm saying I was happier with the 3-blade stainless than the 4-blade aluminum. Performance for the same pitch was about the same. But, I would get at least one prop in per season for repair when I ran aluminum at about $40 a shot. I've been using my Stainless in the same conditions for 3 years without a ding! This has paid for it, in my mind. Also, remember the 4 blade will have more bow-lift then the 3 does. The comparison I am making is between a 4 blade alum I had cupped to 21, and a 3 blade SS 21. Performance was very close, but due to the extra drag of the 4th blade, I lost some RPM. Since the stainless had only 3, and they are thinner, I picked up about 300 rpm on the top end, and a few MPH. I lost just a bit on the bottom end without the extra push of the fourth blade. Also, since the alum blades flexed more, the RPM's came up a little quicker. As far as cruising, Keep in mind my best/economical cruise speed was from the low plane speed (about 20 mph) until the second set of butterflies opened up on the 4bbl carb (about 3500 rpm). With the 19 pitch prop, that gave me a band of 20-27 mph. Not much to play with when cruising. However, with a 21 pitch prop, that stretched to 20-35 mph.... much more room, and a little quicker about getting around without wasting too much gas. Keep in mind, I was still only getting about 4 mpg! In my 18' Maxum w/ 4.3L I pulled 3 tubes with 7 adults and 2 coolers in the boat without difficulty using the Stainless 21. I've been wakeboarding behind that boat as well, and have no reason to go back to alum. I will try a 4-blade SS 20 on the 210SS if I can find one cheap enough. It came with a 3-blade 19 SS, which gave us 59 mph WOT on the test drive. That should pick up the top end a pinch and get great low end performance. I think 60mph is plenty on the water! Hope that helps! |
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