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Old 10-13-2010, 04:20 PM   #1
Lt. JG
Join Date: Oct 2010
Posts: 15
Default Four-blad prop plus whale tail on 2400 SD?

Hello all...

We're about *this close* to buying a 2002 2400 SD (in great shape, new motor with warranty). We're new to boating ownership, but have some experience on the water with various boats. During our test drives, we remarked that it'd be great if it were just a bit quicker to get up on plane.

The salesman commented that we could achieve that by switching from a 3-blade to a 4-blade prop, and adding a whale tail to the outdrive. The cost of the switch is minimal ($250ish, and I can probably get it included in the sale). My question is ... how much of a difference will this make, and is it a recommended change? Should we do both, prop only, tail only, or neither?

Sorry, I don't know the pitch on the original three-blade or the replacement four-blade props...


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Old 10-13-2010, 05:18 PM   #2

Join Date: Apr 2008
Posts: 3,975

What was the boat repowered with?

What type of outdrive is on the boat? (Bravo I, Bravo II, Bravo III?)

Do you happen to know the size and pitch of the prop on there now?

Does the boat have trim tabs?

It's hard to say whether it needs a new prop or not or what size to get. I can tell you that salespeople are infamous for:

"It just needs <yadda yadda>"

"All these boats have <insert problem> problems"

"You can get that part for <insert value> at your local Home Depot/Auto Zone"

"It's a quick 30 min. fix you could do on your own".

The easiest way to tell whether your over propped or under propped would be to do this:

1) Get the boat up on plane.

2) Ge the boat to wide open throttle.

3) Adjust the drive trim accordingly.

4) Compare the actual RPM's to the manufacturers posted RPM range limits.

Overpropped = Actual Max. PM is lower than manufacturers range limit

Underpropped =Actual MAx. RPM is higher than manufacturers range limit.

If the actual RPM is within the max. range limit by teh manufacturer (in your case Mercruiser), then you will be more limited in your options.

Yes a Stainless Steel prop will have less flex and therefor be able to apply more bite to the prop over a aluminum which might have more flex. Yes a 4 blade will get you more bite than a 3 blade. I would be extrememly hesitant about putting a whale-tail on the boat. extrememly hesitant. However, more info is really needed to answer the question responsibly.

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Old 10-13-2010, 05:28 PM   #3

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Join Date: Nov 2005
Location: Everett Wa
Posts: 4,681

imho...and since I used to own that size boat a number of yrs ago...I'd NOT add the whale tail....reason is there will be minimal assistance in getting on plane but will probably cause some corrosion problems later on and stress the anticavitation plate more than it is needed...meaning I've seen chunks taken out when the whale tail broke...

the 4 bladed prop is a good suggestion but it needs to be in the right pitch range so that your RPM wot is in the manufacturers recommended range....learn to use the trim tabs...if you still have problems getting on plane...get larger tabs....but imho...stay away from the whale tail....more trouble than they are worth for miminal assistance...the sales guy is just feeding you a bunch of garbage info..

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Old 10-14-2010, 02:24 AM   #4
Lt. JG
Join Date: Oct 2010
Posts: 15

Thanks all for the answers. As for the questions I was asked, the engine is a Mercruise 5.7L with Thunderbolt ignition (250hp). The max RPM at WOT is listed as "4400 to 4800," but I haven't had a chance to test it on the water with the current prop.

I don't know the outdrive or prop pitch; I've asked the dealer and will post any info he provides.

Sounds like the whale tail is a definite 'no,' and the prop may or may not be a good idea.

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Old 10-14-2010, 10:30 PM   #5
Lt. JG
Join Date: Oct 2010
Posts: 15

The current three-blade prop is a 17 pitch.

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