Moderated Discussion Areas
ContinuousWave: Whaler Performance
|Author||Topic: Outrage prop|
posted 04-24-2000 03:19 AM ET (US)
Does anyone know what the performance differences are between a four bladed prop and a three bladed one on an 18.5, '81, Outrage, with a 150 Merc? I'm using a 17" three blade now, and it peaks out at about 5600 rpm. I would like to be able to stay on plane at a lower rpm. I drops off at about 2800-3000 now. I've read that a 4 blade will keep a boat on plane at lower rpm's, but I'd like to get that information from someone who has actually used one on a rig such as mine. I've also read that there is less steering torque with a 4 blade. Is that true? Top speed is not my primary concern, but boat control in ocean waves, especially the following kind, is. Would a 4 blade be better than a 3 for me? If so, should the pitch stay the same? Help will shore be 'preciated. Russ
posted 04-25-2000 07:03 AM ET (US)
Russ, here are some prop observations that may help you! You can have the perfect hull and the best motor and the wrong prop will ruin it! A correct prop is one that allows the engine to achieve rated max rpm with intended load. This is important for performance and also is good for the engine.
Overreving or underreving can cause engine damage. Generally speaking, an inch of pitch will net 200 rpm, either up or down! So if you need to gain, for example, 400 rpm, you would need to go down 2" in pitch; if you needed to loose 600rpm you need to go up 3" in pitch,,, etc. Number of blades will change performance in the following way... More blades results in less percentage slippage and should give better mid-range accelleration, about same hole shot and lower rpm at WOT (assumming that pitch is held constant) and maybe a little less top speed. More blades will allow you to raise motor higher on transom. The style of blade is important and a general purpose design usually works best! Beware of some 4 blade props that are designed for "bow lifting" as these props have high rake blades and use a lot of power in trying to lift the bow (bass boat stuff). These high rake props will kill performance if hull is not designed for "air time".... and yours isn't! Beware of prop "hype"! Sounds like you have a good prop and can turn correct rpm so maybe to stay on plan at a lower speed you need to consider trim tabs and/or a
fin (DoelFin)! The tabs will allow you to adjust bow up/down attitude to stay on plane at slower speed (also will allow side to side trim while underway) and the fin will give a little lift as stern starts to settle back down... No magic solution that I know of! Happy Whalin'...... Clark
posted 05-02-2000 04:01 AM ET (US)
Thanks for the reply, Clark. I've given up on the Magic 4 Blade Propeller idea. I see them on bass boats, but as you pointed out...I don't have a bass boat. I'll investigate those fin gadgets, tho. Russ
posted 05-09-2000 04:16 PM ET (US)
Russ - I've got a doelfin on my 18'5" Outrage with a 150 Johnson/17"Pitch. Comes right out of the water and highly recommend putting one on.
posted 05-09-2000 11:55 PM ET (US)
Russ, I own a 3 blade (Mirage) and a 4 blade (Offshore).
I love the Offshore - the 3 blade has become my spare.
IMO With the exception of top end (I'm not much of a speed freak - boats fast enough) the 4 blade whoops the 3 in every way.
posted 05-11-2000 03:56 AM ET (US)
Louis: Is your 4 blade the same pitch and diameter as your 3 blade? Is the 4 blade any better than the 3 in following waves. I ply the western Strait of Juan de Fuca where the combination of tides and wind can create some rather large, steep ones. So,I was wondering if a 4 bladed prop, or maybe a DoelFin, would give me better control. Thanks for the comments. Russ
posted 05-11-2000 06:03 PM ET (US)
Mecury makes three types of 4 blade props. Two of them, the "Trophy" and the "Revolution", are high performance bass & go-fast boat props that Clark is referring to, and not recommended for Whalers. Mercury does advertise, however, that for the mid-size gearcase (75-125HP), the Trophy does eliminate steering torque. The four blade "Offshore" prop that Louie is referring to is probably what you want for a Whaler, 135hp & up. I see a lot of these in Southeast FL and they seem to run very well for offshore boating, although a Merc prop guy tells me they're not quite as fast (top end speed) as a "Mirage". Both supposedly provide excellent holding in rough water. I have noticed that Whaler's new Outrage models, factory rigged with V-6 Mercs (of course!), come with either a Mirage or Offshore prop. All of Mercury's props, incidentally, are now designed to fit any brand of engine.
posted 05-14-2000 11:24 PM ET (US)
Russ, we regularily fish juan de fuca as well. The Offshore (19P) blade gives me better control especially in steep chop or big swells. The Offshore shines in big swells - over 10 feet and it really becomes noticable! I also find it more responsive and better at maintaining speed up or down the swells. You will lose a couple miles at the top-end, but IMO its the best rough water prop.
PS Reverse is not as pronounced, so go slow around the dock till you get used to it (if you decide to go with the offshore).
posted 04-26-2001 12:39 AM ET (US)
posted 04-26-2001 05:01 PM ET (US)
In the same vein, what 4 blaed prop(s) are compatable with 1980's Johnson 235? I currently have a nodescript elephant ear, and would like to try a 4 blade prop.
posted 04-26-2001 05:04 PM ET (US)
Anyone else notice that lhg's latest post here is marked "posted 04-26-2000 12:39 AM ET (US)"?
Although now that I'm on the "reply" page it says "posted 04-26-2001 12:39 AM ET (US)".
If I back out of here and refresh it still shows last year so I'll post this to see what happens.
posted 04-26-2001 06:00 PM ET (US)
Very observant, Barry. I notice that all three RECENT posts show year 2000! JimH, can you help us out here, or just a software glitch?
Larry, for your application, I would get a 4 bladed Mercury "Offshore" prop (about $400 most places), with hub for OMC. For a single 235 on a 25 outrage, this prop will give you what you need. These are the props that usually come with the new BW Mercury equipped Outrages. See description on mercurymarine.com. They are specified for heavier boats (relative to available HP - which is your condition) and have agressive holding for offshore conditions, plus give overall hull lift to aid performance. For less money (about $170), you can get a four blade aluminium as an alternative, called an "Alpha 4". Have no experience with this new aluminium design.
posted 04-27-2001 07:08 AM ET (US)
What seems to be happening with these over-1-year-old posts:
If an old posting is revived by someone adding a new reply to it, the software appears to get confused and appends the wrong date to the post.
There is not much that I can do about it at the moment. The old posts still remain available, they just aren't showing up in the topic listings. Maybe a separate index to the real old gems of discussion is the answer.
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