Non-bertram, dual outboard prop/planing question

Face · Post by **Face** » Jul 25th, '10, 14:50

I will post this on the continuouswave site as well but I'm curious what you guys think about the following.

My dad has a 27' Whaler CC Cuddy Cabin with twin 250 Etecs (3rd set of motors over many years). He's in the market for new props and new spare props as he has spun the hubs in his main props. Apparently they can only be re-hubbed so many times.

My question is: is there a general rule for determining what pitch prop would allow us to get on plane with one motor? As it stands now one motor can almost get the boat on plane. If we lose a motor at sea it would be nice to change to a spare prop of different pitch and get home at speed.

He currently runs 2 4 blades (4x14x21) at 5500rpm and 2 3 blades (14 3/4 x 17) at 6000 rpm. 42mph and 44mph respectively. The 4 blades seem superior in many ways with this boat so that is probably what we will go with.

Any thoughts on spare prop pitches? They are counter-rotating and therefore we will need 2 spares.

captbone · Post by **captbone** » Jul 25th, '10, 21:52

The ideal prop to plan off with a single engine would be a 15pitch Mirage Plus or a 13 pitch Mirage Plus. These are large diameter round ear wheels that are designed for large singles. The Enertia prop is also another great choice but harder to find cheaper.

But there is just no need to get those props. All Mercury props come with an interchangable hub system that can be changed by the user in minutes. If you spin your hubs, you pull the prop off and slip in a new plastic hub. Mercury props are unbeatable and with the right hub fit Evinrudes. Their inchangable hub design eliminates the current issue with hubs or the need to carry spare wheels.

Whaler1777 · Post by **Whaler1777** » Jul 26th, '10, 01:02

I dont think youre going to get that boat up on plane with a single engine... I had a 99' 28 conquest with twin 250 ox66's that wouldnt do more than 8kts on a single engine, your boat may be lighter though...

In Memory Walter K · Post by **In Memory Walter K** » Jul 26th, '10, 06:43

When you're down an engine and coming back on one, you're putting a big strain on any engine trying to get your boat up on plane on one. That's asking a lot of it. I would recommend taking more time getting back IMHO.

Face · Post by **Face** » Jul 26th, '10, 10:13

Maybe I'm being too optimistic but the boat can almost get on plane on one motor right now. This is not something we do on a regular basis as it is obviously hard on the motor but we have tried out of curiosity.

The advice I received on continuouswave.com was that the general rule for running on one motor is to go down in pitch 4 inches. The guys on that site seem to think it will plane on one and one guy says his 27 with whaler drive and (2) 225 fichts will plane on one with his regular props and careful use of trim tabs. I'll leave the decision to my dad but thanks for the input.

AndreF · Post by **AndreF** » Jul 26th, '10, 10:19

I had a 27 Whaler w/225 Mrec's. Great big DITTO on Walter's remarks. That's asking for heat, heat and more heat on that one engine and when the buzzer sounds, it's like taps- too late already.

STraenkle · Post by **STraenkle** » Jul 26th, '10, 12:39

Well if you can find them, The Torque-Shift prop is a way to do it. They shift pitch based on RPM and load on the prop (like 12inch pitch continiously to 23 inch pitch). Land and Sea in New Hampshire designed and built them, but I think they sold the rights a while ago. Neat idea.

captbone · Post by **captbone** » Jul 26th, '10, 13:39

You will be fine and will be able to plane off on a single with a 13pitch or a 15pitch prop.

As long as the engine is not lugging and can meet the recommend RPM range it is absolutely fine and doesnt shorten the life of the engine. The engine does not know if it is on a 21ft Superboat or a 40ft Barge as long as it reaches recommended rpm. I have run engines for long periods of time tied to the dock at WOT with an old OMC test wheel or even an old prop that is cut down with a grinder.

The 13 or 15pitch wheel will allow you get your RPMs into the correct range while providing the thrust you need.

I have seen a 28ft Bertram with a single 250hp Yamaha on a bracket that runs fine and breaks 30mph.

Just my 2 cents

Its all about correct propping.

Carl · Post by **Carl** » Jul 26th, '10, 13:46

captbone wrote:You will be fine and will be able to plane off on a single with a 13pitch or a 15pitch prop.

As long as the engine is not lugging and can meet the recommend RPM range it is absolutely fine and doesnt shorten the life of the engine. The engine does not know if it is on a 21ft Superboat or a 40ft Barge as long as it reaches recommended rpm. I have run engines for long periods of time tied to the dock at WOT with an old OMC test wheel or even an old prop that is cut down with a grinder.

The 13 or 15pitch wheel will allow you get your RPMs into the correct range while providing the thrust you need.

I have seen a 28ft Bertram with a single 250hp Yamaha on a bracket that runs fine and breaks 30mph.

Just my 2 cents

Its all about correct propping.

Ditto...the trick is not just to get on plane but to be able to bring the motor to the recommended WOT as well. If not your just going to destroy the motor... thinking its best to come home slow, then not come home at all...at least under your own power.

Face · Post by **Face** » Jul 26th, '10, 14:07

Captbone, I remember the test prop you refer to from my first job at 14. My boss ran the hell out of some motors at the dock with that wheel. I find this to be an interesting and expensive topic. It's much less expensive with input from others that minimizes prop testing. Between this site and continuouswave dad and I are much better off. Thanks for the opinions guys.
-Joe

Face · Post by **Face** » Jul 26th, '10, 14:13

captbone wrote:The ideal prop to plan off with a single engine would be a 15pitch Mirage Plus or a 13 pitch Mirage Plus. These are large diameter round ear wheels that are designed for large singles. The Enertia prop is also another great choice but harder to find cheaper.

But there is just no need to get those props. All Mercury props come with an interchangable hub system that can be changed by the user in minutes. If you spin your hubs, you pull the prop off and slip in a new plastic hub. Mercury props are unbeatable and with the right hub fit Evinrudes. Their inchangable hub design eliminates the current issue with hubs or the need to carry spare wheels.

Back to your original point of just changing the hubs at sea, BRP has a similar "TBX" system. Let me ask you this. First off is it true that the more traditional props can only be rehubbed so many times? This seems to be the case with our props which visibly appear to be in great shape.

Additionally, can the new merc/bombardier interchangeable hub systems be rehubbed indefinitely?

The only downside to just changing hubs would be an engine failure vs a propeller failure.

captbone · Post by **captbone** » Jul 26th, '10, 15:59

I dont really agree with the statement that traditional props can only be rehubbed so many times unless something is damaged. I just dont see the stainless steel walls deforming or not allowing a new hub.

The hub is pressed into place and is actually difficult to achieve factor results. I know that Yamaha is having big problems with replacing their hubs because everyone uses aftermarket hubs.

I would get a second opinion from another prop store and make sure they sure an OEM hub.

The Mercury and Evinrude interchangable hub system is great and revolutionary. The inside of the prop is square and a square plastic insert goes into the prop. A metal splined insert is in the middle of the plastic hub. They just sit relatively loose in the prop. When you hit something it rounds off the square plastic hub. You simply remove the prop, replace the square plastic hub and put it back on. You can rehub these forever and you can check the hub in the winter to see how its doing.

Let us know how you make out.

bertram31.com

Non-bertram, dual outboard prop/planing question

Non-bertram, dual outboard prop/planing question

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