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| Author: | 1baddoggy [ Mon Jun 12, 2017 4:10 pm ] |
| Post subject: | Selecting new propeller |
Hello all. I'm trying to pick a new propeller that will help get on plane a bit quicker, especially when pulling a tube. I'm on Mercury's website, and there's a couple questions it's asking me that I'm unsure of. It's asking me for the gear ration of the outdrive. I know I have an Alpha 1, but I'm not sure how to determine the gear ratio. It lists 1.62 and 1.81 as options. Additionally (for best results), it's asking for Wide Open Throttle RPM's and Current Top Speed. I can easily determine the WOT RPM, but Top Speed changes frequently depending on current, wind, load in the boat, etc. Is there a good way to determine this? Do I just go out where there is no current or wind with my average weight load and see what it tops out at? For bonus points... would a hydrofoil combined with my factory aluminum prop make more difference than a more aggressive SS prop? Thanks! |
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| Author: | Cap'n Morgan [ Tue Jun 13, 2017 6:38 am ] |
| Post subject: | Re: Selecting new propeller |
What size prop do you currently have ? 14-1/4 x 19p 3 blade ? |
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| Author: | 1baddoggy [ Tue Jun 13, 2017 8:07 am ] |
| Post subject: | Re: Selecting new propeller |
I currently have an aluminum 14 1/4 x 21p 3 blade. |
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| Author: | Cap'n Morgan [ Tue Jun 13, 2017 8:16 am ] |
| Post subject: | Re: Selecting new propeller |
I had the same prop on our boat. I switched to a 14 x 20p 4 blade aluminum and it pulled great. Barely lost any RPM at WOT and only 1-2 mph top speed. |
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| Author: | rpengr [ Tue Jun 13, 2017 3:07 pm ] |
| Post subject: | Re: Selecting new propeller |
Current and Wind can be negated by doing a WOT run in two (opposite) directions. Then take the average of the two. As much as possible, this should be directly with the current and against the current (not sideways to the current). I think that Speed at WOT is usually measured with a relatively light load, such as 1/2 tank fuel and maybe 2 people in the boat. 1baddoggy wrote: For bonus points... would a hydrofoil combined with my factory aluminum prop make more difference than a more aggressive SS prop? Some people have experienced bad handling behavior when using a hydrofoil with the Four Winns hull design. |
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| Author: | 1baddoggy [ Thu Jun 22, 2017 8:23 am ] |
| Post subject: | Re: Selecting new propeller |
Ok, finally got out and tested my WOT RPM's yesterday. At WOT I was doing 3900RPM and about 39MPH. Based off this information and my current propeller, I'm looking at swapping to a 14.625" 17p Mercury Revolution 4 or a 13.5" 17p Mercury High Five. I read people rave about the High Five's, but I think the Rev 4 would still be a huge improvement and be a little better all around. I'm dropping 2 pitch sizes, going from 3 to 4 blade and from aluminum to stainless steel. Thoughts? |
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| Author: | zims1993 [ Thu Jun 22, 2017 1:20 pm ] |
| Post subject: | Re: Selecting new propeller |
Your WOT RPM's seem rather low, what is the range WOT RPM for your engine? |
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| Author: | 1baddoggy [ Thu Jun 22, 2017 1:26 pm ] |
| Post subject: | Re: Selecting new propeller |
Supposed to be 4400-4800 WOT |
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| Author: | rpengr [ Thu Jun 22, 2017 2:54 pm ] |
| Post subject: | Re: Selecting new propeller |
Yes, 3900rpm WOT is Dangerously low. (Dangerous in that it could cause valve damage if run at higher power for enough time) However, I'm not sure if you might be going too far by dropping to 17p. Should be great if holeshot is your priority. 19p may be better overall. Usually going to SST will get you some more RPM by itself. Other opinions? |
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| Author: | 1baddoggy [ Thu Jun 22, 2017 3:16 pm ] |
| Post subject: | Re: Selecting new propeller |
So with being at 3900 RPM at WOT, I may have an issue I need to get looked at? Perhaps the tach is off... I didn't pay attention to what my idle RPM is. |
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| Author: | 1baddoggy [ Thu Jun 22, 2017 8:27 pm ] |
| Post subject: | Re: Selecting new propeller |
I'm idling at 700 RPM. |
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| Author: | TheDanceII [ Fri Jun 23, 2017 7:24 am ] |
| Post subject: | Re: Selecting new propeller |
For every inch of pitch you go down, in theory you will increase rpms by 150 given the same design prop. In theory you would go from 3900 to 4500 rpms going from 21 to 17. However: 1) You are lugging the engine and not making proper power 2) You are going from an aluminum 3 blade to SS which will make a big difference in performance and efficiency 3) You are going to a 4 blade (or 5 blade) which will reduce rpms slightly over the same pitch 3 blade (which is why the 4 blade has a slightly smaller diameter to compensate). Bottom line, Make sure you can return the prop if undamaged within 30 days for a swap to a different pitch. The 17 in theory will be correct but may not be since your changing so many things at once. |
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| Author: | Surface Interval [ Sat Jun 24, 2017 9:20 pm ] |
| Post subject: | Re: Selecting new propeller |
Generally, boat manufacturers prop a new boat so it will be in the upper half of the max rpm range. My '95 190 horizon would turn very near the top end of the 4200-4600 rpm range at top end. I assume the same is/was true for your boat. If you are 800rpm low and 8 mph low, I would start by verifying that the engine and drive are operating properly. Your boat has the factory sized 14.25" diameter X 21" pitch. I would wonder what changed to cause the boat performance and engine performance to be so far from top end rpm and speed listed by Four Winns for that model of boat? The drive ratio and model number should be on the data tag on the outdrive, at least it is on the Volvos. The number is how many engine rpms equal 1 prop rpm. This is determined by the gear set in the outdrive. 1.60:1 would be 1.6 engine revolutions per 1 prop rpm. Gages have been known to read incorrectly. Verify their accuracy. You can use another tach or a digital timing light with tach readout to verify. Your speedometer can be verified by a gps or gps readout on your smart phone. My current boat had a tach that was reading low at times, causing the operator to push the throttle more. The end result was that the engine was cruising at 200-300 rpm faster than the tach was indicating, and the speedometer was showing about 4 to 5 mph faster than normal cruise for that indicated rpm. The new replacement tach was even worse. It read 200 rpm low at idle and about 800 rpm low at cruise speed. The second replacement tach is right on. Thank you to Four Winns for the product support. As I recall, the general guideline is 150-200 rpm change for each 1 inch of pitch on the same make/model of prop. Changing 4 inches of pitch should make maybe 800rpm difference. But this usually comes a a loss of top speed, which is already low. I bought a Stainless Steel Stiletto-brand prop in the same size for my 190 Horizon. There was no detectable difference in performance between the OEM Volvo aluminum prop and the stainless prop. If you are changing to more blades, the recommendation is to reduce diameter. Think about the total surface area of the blades. Larger blades are usually found on props for larger heavier boats, and smaller blades for lighter boats. Adding a blade or two will be harder for the engine to turn, so each blade is usually smaller and possibly shorter. There are a lot of differences between prop brands and models. Differences can include blade surface area, contour, rake angle, cupping the trailing edge, double cupping, etc. Understand what you are buying, and what the return policy is. |
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| Author: | 1baddoggy [ Sat Jun 24, 2017 10:08 pm ] |
| Post subject: | Re: Selecting new propeller |
I put on a 17p aluminum 3 blade prop today and it put me right where I'm supposed to be. About 4500 RPM at WOT. I also jumped up to 42mph. |
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| Author: | Surface Interval [ Sun Jun 25, 2017 7:49 am ] |
| Post subject: | Re: Selecting new propeller |
It still sounds to me like you are not getting full power. Four Winns specs for that set-up are 48 mph at 4500rpm and 50 mph at WOT with a 21" pitch prop. You decreased pitch 4" and the rpm rose 600 rpm to 4500. Unless the engine is not performing or someone has changed gear ratios in the outdrive to something noticeably lower than the 1.62:1, you should be getting much better performance from the 21p prop. The 17" should be going way over the 4800 rpm redline. I had a similar loss of power situation on my 190 with the Volvo 5.0 EFI when I had an exhaust flapper valve come loose and created a partial blockage in the exhaust. That robbed me of a lot of power. The boat ran smooth but struggled to get on plane. RPM was 500 low and top speed was 10mph less. I am assuming that you are trimming the outdrive up at least a fair amount at top end. Trimming too much will either cause the bow to "porpoise" or the boat will lose speed. Not trimming the outdrive will cause the boat to not reach top speed or rpm. Regarding the fins, personally I am not a fan. Some fins on some boats work fine, but not all fins are a help on all boats. They may help get on plane, but some can cause some really wierd handling characteristics, as I experienced on the 190. |
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