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ContinuousWave: Whaler Performance
Another Prop Quandary
|Author||Topic: Another Prop Quandary|
posted 05-02-2001 02:34 PM ET (US)
I am looking to re-prop my '91 22' Outrage WD with 250 Yamaha V-x.
I think the boat has the original SS teflon coated Yamaha prop on it. I have yet to find any markings on this prop except for some cryptic numbers that have no similarity to prop dimentions.
I have looked at the Mercury web site, and have even become more confused. The Offshore says that it is recomended for twin appications. So I think that is out.
What about the Laser II or the Revolution 4?
I am currently running about 5200 WOT. The teck says that the engine is rated for 4500-5500. I have yet to install my chartplotter/GPS, so I don't have an accurate speed reading @ WOT. My LORAN says 37.8, my sounder says 63.9 and the speedo says 51.
My boat does have an aluminum T top. And I generally run with no more than 3-4 people and most of the 77 gal of fuel it can take.
Since the addition of the Stingray Hydrofoil, hole shot is not a problem. So my goals are to improve top speed and mid-range cruising effincey.
So what are some recomendations for pitch and model?
posted 05-02-2001 03:10 PM ET (US)
Brian - Although I am running Merc Laser II's on my Outrage with twin 200's, I think with a big single you would be better off with either a Mirage or Offshore prop. The big Mercs have a 1.75 gear ratio and the Yamaha has a 1.81, so the Yamaha might require a slightly higher pitch prop than a Merc 250 to go the same speed, or it won't be quite as fast, which is more to my inclination. Also your tee top can take a few mph off top speed easily. I would *GUESS* you want a 19" pitch prop, which should give you a speed range of up to 53. If this is too much, and the boat simply won't go that fast, the 17" will give you up to 47/48. The Merc prop charts show a 17 as too low for a Merc 250 on a boat like yours.
No offense, but I would not have that Stingray on any of my engines. Your engine should be mounted so that the anti-cavitation plate runs about 3/4" above water coming off Whaler Drive, so the thing will be riding in air anyway. If the engines is not raised right now, and the fin is dragging in the water, you are losing speed. But if your engine is installed with a higher "X" dimension, and with the vented Mirage or Offshore prop, you should definitely gain some performance, both in acceleration and top speed. The Mirage and Offshore are great props, and are used on all the new Whaler Outrages with V-6's. The Mirage is a slightly faster prop than the Offshore, but the Offshore holds on better in heavy seas, and provides more total hull lift. Laser props don't seem to be recommended for engines larger than 200HP, and the Revolution is a go-fast boat prop.
posted 05-02-2001 06:34 PM ET (US)
When I use the Mercury prop selector, should I include a couple of extra feet for the WD? Also, I think the Mriage and Offshore props are in the 14" dia. area. Will this fit on the motor?
You see, my problem is that the marinas in my area do not stock these props, and it is a no return situation once I have installed it. And for $625 for the Offshore, and similar for the Mirage, I want to be right the first time.
posted 05-02-2001 07:05 PM ET (US)
Brian - the price quoted to you is too high. I know of a place that sells any style of Merc performance prop, any pitch, for $399.
All of these will fit the Yamaha. A friend has a 19" pitch Merc Laser on his 200HP Yamaha.
I would use the Mercurymarine.com prop selector using TOTAL MAXIMUM weight, instead length. I would also use the Merc 225 EFI as the engine, which should accomodate the slightly different gear ratios between Merc and Yamaha. Don't use the Optimax. In the 225's, the EFI is about 3 mph faster. I have also noted that the prop selector tends to be a little high on pitch, so be sure you load in all the weight, persons, gear, fuel, etc.
posted 05-04-2001 08:36 PM ET (US)
Brian - There is a used (he says excellent condition) 19" pitch Mercury Mirage Plus prop for sale on propswap.com for $250. Search Mercury, Mercury, Mirage Plus and you'll see it. The seller has a Boston Whaler! This site works pretty well. I have sold 2 props there with no problem.
My guess is the prop will have the Mercury hub, so you would have to buy only one additional part to adapt to a Yamaha. Space washer # 12-850076. The other parts of the hub are the same! I believe Yamaha has basically used Mercury's prop shaft design.
You only want the new design Mirage Plus, with the adjustable venting and new blade geometry. The original, older design (not as good) was just plain "Mirage". They do not have the interchangeable hub.
posted 05-04-2001 10:46 PM ET (US)
Thank Larry, I will check it out. I have been wondering about the venting. Can you explain it a bit?
posted 05-06-2001 01:45 AM ET (US)
Propeller hub vent holes (another prop idea invented by Mercury, I believe, with the Laser series) are primarily used on propellers with more aggressive blade geometry, often the "performance enhancing" type for boats that will run to 45MPH or higher. They intentionally induce prop slip (ventilation) on acceleration. I have yet to see them used on the conventional aluminum or SS models. My guess is that the high rake blade geometry of performance props take a bigger "bite" on the water at lower RPM and speeds, so the venting relieves this loss.
Originally, vent holes were a fixed design, probably sized for the average application.
On acceleration, exhaust is drawn out of the vent hole. The amount of aerated water is determined by the size opening. There is one in front of each blade. When the propeller blade strikes this aerated water, it pushes through it much easier than it would through solid water (it slips a little). By controlling the amount of aerated water, you can control how fast the rpm rises on acceleration, getting to a more useable HP range quicker. Once you're on plane, the water now flowing over the vent holes seals in the exhaust, allowing the propeller to again operate in solid water.
My experience using vented props is that they really "dig" if you want them to. Generally, the RPMs will pop right up to 3000, then you feel them REALLY grab as the boat goes past 20 mph and the power comes on. You have to back off the gas quickly, or you'll be doing 45 in no time.
For continuous slow planing speeds, or rough water, they are best minimized or closed up, as venting increases the rpm's needed for planing at low speeds (below 25mph). It doesn't appear to effect idle speed performance.
Vents don't seem to be used much on I/O applications.
posted 05-06-2001 12:11 PM ET (US)
Thanks for the info. Looks like I am leaning twards the Mirage Plus. I just don't think the Offshore is for my needs.
posted 05-06-2001 06:25 PM ET (US)
Brian - not to confuse you further, but hunt around the Forum for some previous discussion on props. Louie Kokinis, of 22 Guardian fame out in Vancouver (see Cetacea pages on his boat), I think has said that he has run both the Mirage and 4 blade Offshore (he has single Merc 225), and likes the Offshore better. Or just E-mail him. He hasn't posted anything lately. He might be of help on pitch also. Also contact Clark Roberts, whose friend has a Whaler Drive 22 Revenge and single 225 Optimax.
posted 05-17-2001 06:29 PM ET (US)
Just an update. I have installed and ran a new Mercury 17" Mirage Plus on my boat. I had the vent holes completely plugged.
What I noticed...
1) Even though I stepped down from 19 to 17 pitch, RPM's only went up about 150. I assume this is from going to a larger diameter prop and added weight.
2) I held a constant 52 mph (according to debth sounder) on flat water. Not much change here.
3) Vibration was cut dramatically.
4) Mid range accelleration was noticeably better.
5) Hole shot was the same.
Thanks for all who helped out.
posted 05-17-2001 07:02 PM ET (US)
I posted a ? regarding a 1999 merc. 200 offshore on a 82 22' outrage. I think it can relate to this post. Is this underpowered? Wish to cruise in upper30s mph and top end @48-50. Is this motor producing more hp than it is labeled as the rumor states that mercs are alittle faster? What prop should I consider to acheive close to this?thanks
posted 05-18-2001 10:40 AM ET (US)
No offense lhg, but the vent holes are behind each blade.
The question I bring, has anyone tried the homebrew approach to venting your stock stainless prop? I started with 1/4" holes, and I'm upto 5/16" on my 13x19 OMC stainless (an original 1985 issue prop, before the advances in prop design). I have had the prop cupped to replace that worn off by the previous owner on sand bars.
posted 05-23-2001 08:02 AM ET (US)
One final note on my new Mirage Plus prop. It has considerably less performance in reverse than the Yamaha SS prop it replaced.
I was in a situation yesterday that required several forcefull back ups, and I really noticed a decrease in reverse power.
posted 05-23-2001 02:34 PM ET (US)
Where2 - I think symantics is the issue on vent holes. The hole is "behind" one blade and "in front of" the next blade. The hole is close "behind" a blade, so that exhaust can be drawn out easier, causing the bubbles to "soften" the water being pushed by the next blade, increasing rpm's and acceleration. With regard to self-venting a standard prop, I have no idea whether it makes sense. May cause too much slippage, since these don't grab as well as a higher rake prop. The propeller companies don't offer vents in standard props, however. There must be some reason for that decision.
Let us know how it works for you.
Brian - glad you're happy with the Mirage prop. As with any higher raked propeller, reverse thrust is reduced, as they have no real bite in the opposite direction. You can tell this just by looking at the blade shape. These things are designed to go forward! That must be why Mercury claims the 4 bladed Offshore model has better reverese holding.
If you want to increase hole shot, open up the vent holes by using a small or medium hole plug instead. I think the Mirages come with solid vent plugs because many of those props are used on Stern Drives also, and they can't use the venting feature. They send out new props with the vent size most often used for a given prop. I have noticed that venting requires a slightly higher RPM to maintain slow planing speeds below 25 MPH, probably because of increased slippage. So you'll have to decide if faster acceleration is worth that trade-off. Your Stingray unit will also hurt acceleration because of the increased drag in the water, until it rises clear of the water as the boat planes out.
Although the Mirage is not advertized as a bow or hull lifting prop, did you notice any difference in hull trim? The boat should be running a little higher on the water.
posted 05-24-2001 07:55 AM ET (US)
Hole shot is not an issue, but I love to tweak, so I will play with the vent holes.
As far as raising the engine, I think it is as high as it can go right now.
With the smaller increase in RPMs, I think I can atribute that to not only throwing a heavier unit, but the wheel is also about 1.5" larger in diameter.
I don't think I noticed any higher running with this new prop. I have yet to have a nice enough day here to spend more than 20 min with it. I will let you know.
posted 05-24-2001 09:01 PM ET (US)
Brian - Where you'll really notice an improvement is how well the prop hangs on slow going in big waves and rough weather.
They're almost impossible to break loose and slip out on you.
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