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Author Topic:   27' Whaler props
Boston1 posted 03-24-2004 10:59 AM ET (US)   Profile for Boston1   Send Email to Boston1  
27 CCC Whaler w/ T225 Mercs (1994) turning 15 X 19 SS Mirage props. The boat has a hard top without a canvas enclosure. Currant WOT is 5000. I plan on putting an enclosure on, so I will need to re prop to get the RPMs up. .

When powering up to get on plane, both props ventilate. Can anyone suggest a prop that will bite and eliminate slippage?
Also, any suggestions on the prop size?

Thanks

bwguardian posted 03-24-2004 12:57 PM ET (US)     Profile for bwguardian  Send Email to bwguardian     
BOSTON1,

YOU SHOULD BE ABLE TO TURN MIRAGE 15 1/4" X 17" MIRAGE PROPS. THOSE 19" SHOULD BE 15 1/2" UNLESS THEY HAVE BEEN WORKED. DO THEY HAVE THE VENT HOLES AT THE BASE OF THE BLADES? THE VENTILATING PROBLEM COULD BE SEVERAL THINGS SUCH AS ENGINE MOUNTING HEIGHT. HOW LONG HAVE YOU HAD THE BOAT WITH THESE ENGINES AND PROPS? THE MIRAGE PROPS ARE ONE OF THE BEST ON THE MARKET, THE ONLY OTHER PROP YOU MAY CONSIDER IS THE REVOLUTION 4'S.

MY OLD 25' OUTRAGE WITH TWIN MERCURY 150'S SPUN HIGH FIVE 19'S. MY NEW TO ME 27' C.G.P. WITH TWIN MERCURY E.F.I.'S WILL SPIN MIRAGE 17'S.

CALM SEAS...

Boston1 posted 03-26-2004 02:19 PM ET (US)     Profile for Boston1  Send Email to Boston1     
BW
Thanks for the response. I bought the boat the end of last summer and put about 50 hours on it. In addition to venting when getting on plane, it also vents when running in a following sea.
The p/ns from the props indicate that they are 15 x 19, but could have been worked on.
The motors are mounted as low as they can go.

Does your 27 have trim tabs?
How far apart (prop shaft to prop shaft) are your motors? Ill measure mine this weekend.

LHG posted 03-26-2004 02:35 PM ET (US)     Profile for LHG    
There is no way the Mirage props would be ventilating with engines all the way down. Something is not right here.

First of all beware of "reworked" props. The engineers at Mercury do it right (widely regarded as the best outboard/sterndrive props in the world) and aftermarket prop work is rarely by a prop engineer.

Be sure your Mirage props are the redesigned "Mirage Plus" models, with interchangeable hubs and vent plugs. The earlier Mirage props did not have vents, nor run as fast.

However, I would buy the hot new Revolution 4 props instead of Mirage Plus, in 17" pitch, and raise your engines up a hole or two. These offer superior holding and acceleration, strong mid-range, and are just as fast top end. I have noticed that BW is now using these on the big Outrages with twin 225 and larger engines.

Peter posted 03-26-2004 05:48 PM ET (US)     Profile for Peter  Send Email to Peter     
According to Chuck Bennett: for the 27 Whaler with Whaler Drive typical engine height would bring the anti-ventilation plates running in line with the bottom of the boat. Center line distance on the 27' Whaler drive would be 32" on center. Toe in: Measure the distance between the prop centers and forward edge of the gearcase at the ventilation plates. The measurement at the forward edge of the gearcase is to be 1/2" to 3/4" less than the prop center measurement.

I suppose that even the best-in-class Mirage Plus factory props from Mercury could ventilate if toe-in wasn't dialed in right.

LHG posted 03-27-2004 03:12 PM ET (US)     Profile for LHG    
I am confused about Chuck Bennett's description of toe-in.
I have always thought that it meant the prop nuts were closer together than the engine mounting spacing, which means the prop wash converges. I think this gives a slight increase in speed.

I was also assuming this 27 was a traditional notched transom model, since no WD was mentioned?

This summer we ran into a 28' Grady owner with a pair of Yamaha 250 OX 66's on it. I noticed he was running Merc Mirage Plus props. I asked him about this, and he said that he was getting a lot of slippage with the Yamaha SS props that came on the boat, and his dealer suggested the switch to Mercury Mirage models. He said they hold much better and run faster, and was very pleased with them. Now I think Mercury is recommending the Revolution 4 props as an even better solution. All of the 320 Outrages I have seen seem to be using them, either with the twin 250 Optimax or 250 Verados.

hardknots posted 03-27-2004 06:07 PM ET (US)     Profile for hardknots  Send Email to hardknots     
Boston1
I tried a couple of options and the best performance was with a couple of 14 1/4 X 17, 4 blade ss turbo propeller from Precision Propeller Inc. They are designed with progressive pitch blades. Good luck.
Ricky
Boston1 posted 03-29-2004 05:22 PM ET (US)     Profile for Boston1  Send Email to Boston1     
Thanks for all the replies.

My 27 is a notched transom. Prop shaft to prop shaft measures 26 apart. The props are Mirage (p/n 48-13700-19 & 48-13700-19). I do not believe they are Plus (no vents etc).

It seems counter-intuitive to raise the engines if I am having the props slip while getting on plane. Father apart or lowering them seems like the answer (but a lot of work). The answer I am hoping for is to replace the props.

I hope the additional information is helpful.

Peter posted 03-29-2004 06:03 PM ET (US)     Profile for Peter  Send Email to Peter     
How do the anti-ventillation plates match up with the bottom of the hull? Are they significantly above?
bwguardian posted 03-29-2004 06:05 PM ET (US)     Profile for bwguardian  Send Email to bwguardian     
Boston1,

What is the measurement as taken at the front of the engine lower unit casings (nearest the transom)? Also, is the left hand rotating lower gear housing on the port side?

Calm Seas...

LHG posted 03-29-2004 06:20 PM ET (US)     Profile for LHG    
I think the 27 hull was designed for 28" engine mounting centers, so with 26" you're already getting some elevation.

My guess your problem is the older design Mirage props. Mercury has said the "Plus" models were a big improvement.

I would go with a set of 17" Revolution 4's, running medium sized vents. They really hang on and won't slip. You'll get better acceleration and top end. These are going to cost about $425 each. I'm sure a set of 17" Mirage Plus can be found used if cost is a concern. They will work fine also.

Boston1 posted 03-31-2004 04:49 PM ET (US)     Profile for Boston1  Send Email to Boston1     
BW- From the front of the gear case to front of gear case is 26, same as from shaft to shaft. Should the engines be toed in and could the lack of a toe in cause some of the slippage problem?

LHG-Thanks fro the prop recommendation, I am going to look into them and let you know how new props work.

Peter-I think the anti vent plates are a little above the bottom of the boat and that would coincide with the theory that the engines should be mounted 28 apart. If swapping out the props solves the problem, it would be easier than re-mounting the engines.

Thanks

Peter posted 04-02-2004 09:40 PM ET (US)     Profile for Peter  Send Email to Peter     
Larry, I was just reading a service manual chapter on twin outboard setup and Chuck's description of toe-in is consistent with that as I would expect.

Toe-in = gearcase noses closer together than prop nuts by 1/4 to 3/4 inch.

Toe-out = prop nuts closer together than gearcase noses by 1/4 to 3/4 inch.

Interestingly, it says that most conventional twin outboard setups should be toe-in but set-back brackets often use toe-out instead.

Peter posted 04-02-2004 09:44 PM ET (US)     Profile for Peter  Send Email to Peter     
Boston, as I recommended before, check to make sure your toe-in is within spec which is typically a range of 1/4 to 3/4 inch. Too much toe-in will cause ventilation among other things. I think as little toe-in as possible is probably better for traction.
LHG posted 04-03-2004 03:30 PM ET (US)     Profile for LHG    
Peter - thanks for the clarification on toe-in, toe-out. I guess I've had it wrong all these years, but boy am I confused, always setting mine for toe-out when in reality I was thinking toe-in. When I talk to the Mercury guys at the Stuart FL Rendezvous, I'm going to ask about all of this.
I know Mercury puts out a huge, telephone book like, rigging manual that discusses all of these things.

But I think the pro's have the terminology wrong.

If one stands looking down at your toes, (assuming we can see them) translating to a gearcase, I would assume the toes = props. So if am standing "toes-in" (pigeon toed), I would assume that means "toe-in". How they get that to mean toe-out is a mystery. I think their terminology is backward! Seems more like "heel-in" (toe-out) and "heel-out" (toe-in) makes more sense. Or even better, converging or diverging prop wash to really perfectly describe it. I'm getting dizzy.

Moe posted 04-03-2004 07:16 PM ET (US)     Profile for Moe  Send Email to Moe     
Larry,
Toes are on the front of the foot and heels are on the rear. :) Toes = front of lower unit and heels = props.

--
Moe

Peter posted 04-03-2004 07:21 PM ET (US)     Profile for Peter  Send Email to Peter     
Well the boating industry probably borrowed the terminology from the automobile industry and if they look at it from the forward motion perspective, from leading to trailing edge/side, much like you would with the front wheels of an auto, they have used it consistently.

Your definition also makes alot of sense, however. Guess it all depends on the frame of reference. According to the manual I was looking at, your toe-out setting might actually be better than a toe-in setting for your set back rigs.

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