2001 28 Conquest re-power

Optimizing the performance of Boston Whaler boats
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2001 28 Conquest re-power

Postby MaxEriksson » Tue Dec 25, 2018 12:39 pm

Hi All. I'm new to this forum. I'm currently looking at a 2001 28 Conquest in really good condition. It still has the original 225 OptiMax engines. The boat has had two owners, and there are service records for every year at an authorized Mercury dealer.

I've read a lot about the boat on this and other forums. My biggest concern is the acceleration and keeping on plane at lower speeds. The most common solution seems to be to get the Revolution4 propellers; the boat currently has three-blade Mirage propellers.

I don't care that much about top speed; acceleration and maintaining plane at lower speed is more important to me.

I just stumbled on a set of two 2008 OptiMax 300XS engines with 350 hours. Thsee engines' service history is not as good as the 225 OptiMax engines.

But I might be able to buy these 300VS engines and sell the current engines, and it won't cost me more that $1,500 to $2,500.

Any recommendations from you guys?

PS. I'm from Sweden and these boats are really rare here.

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Re: 2001 28 Conquest re-power

Postby jimh » Wed Dec 26, 2018 8:42 am

In general, I think an upgrade to c.2008 Mercury OptiMax engines from c.2001 OptiMax engines would be an improvement. There was a new generation of OptiMax engines, called OptiMax The Next Generation or OptiMax TNG, which occurred in c.2006. See my article about this evolution:

OTNG--OptiMax The Next Generation

Also see this thread:
OptiMax G2--The Globe Motors

While Mercury described the changes as "dramatic," I don't really see them as worthy of that adjective. The most significant change was to bring the VERADO gear case to the 300-HP engine, replacing the Fleetmaster gear case, which was really a racing gear case. There was also a minor reduction in noise claimed to have been achieved. And new cowling design.

Mercury has used the model designation "XS" on a number of engines, and I don't have a clear understanding of exactly what the "XS" is supposed to denote. It certainly was a marketing branding, giving the engine different embellishments on the cowling. It might also be a reference to switching back to the Fleetmaster racing gear case. The "XS" model variants have generally been a branding to enhance sales to boaters with very high-speed boats, what we call "bass boat" and go faster than 60-MPH.

I don't know if an OptiMax 300XS is the perfect engine for twins on a CONQUEST 28, but at the modest cost you mention to acquire them and sell the old engines, just on the basis of jumping to c.2008 engines--which should be in the "next generation" of production--would be an advantage.

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Re: 2001 28 Conquest re-power

Postby Ridge Runner » Wed Dec 26, 2018 12:30 pm

As a former owner of a 2002 295 Conquest (the same boat - ~31' in length, 6,600LBS dry weight, 10'4" beam), going up 150hp and keep the weight the same is a good move. I believe that you would be much happier with the performance of twin OptiMax 300XS'. This is a big boat with a wide beam and a notched transom. Revolution4 propellers are a must for this hull, as she is difficult to hold on plane at lower speeds and a bear to back into a tight slip with any kind of wind or current. There are some good threads on the old forum about this boat.
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Phil T
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Re: 2001 28 Conquest re-power

Postby Phil T » Wed Dec 26, 2018 3:09 pm

Here are pages of threads regarding the Conquest 28 from the archived old forum.

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Re: 2001 28 Conquest re-power

Postby MaxEriksson » Fri Dec 28, 2018 5:40 am

Hi All--Thanks for your responses. I wasn't able to get the 300XS' for a good price, a lot of people started bidding on them. I'll stick with the OptiMax 225. I think that I'll upgrade to REVOLUTION4 propellers according to recommendations in this forum.


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Re: 2001 28 Conquest re-power

Postby jimh » Fri Dec 28, 2018 4:17 pm

MaxEriksson wrote:...I'll upgrade to REVOLUTION4 propellers...

MAX--the REVOLUTION4 propeller is a big and heavy propeller. You will find it shifts with quite a KLUNK if you use the standard FLO-TORQ-II hub kit. Give some consideration to getting the torsion flexing improved hub kits like a FLO-TORQ-IV. Check with a good Mercury propeller and hub kit supplier for more advice.

There is a very good article about FLO-TORQ adapters at

FLO-TORQ Adapters

Also, the FLO-TORQ IV adaptors WILL add some wobble to the propellers. This is discussed at length in another thread. See

Flo-Torq IV Hub Decreases Loud Clunk, But Has Wobble

I recommend you read that thread before going with FLO-TORQ IV. When you read the thread, pay attention to the comments about the hub and how it works as presented by Tom W. Clark and dated 10-31.2007. Tom actually understands how the hub works, has experimented with modifying the hub, explains HOW the torsion flexing works, and how there is an inevitable fore-and-aft loose fitting of the propeller onto the adaptor and propeller shaft with the inevitable wobble that results. Here is an excerpt from the thread:

Tom Clark wrote:The design of the Flo-Torq III and Flo-Torq IV hub kits has confounded me for a while. They are excellent at reducing both shift clunk and propeller rattle on my engines. But the wobble they allow does not sit well with me.

I found that when mounting an out-of-the-box Flo-Torq III or IV kit on my engine, there is a fore and aft movement along the propeller shaft (or along the hub insert itself) that means the propeller is not really fixed relative to the propeller shaft as we would normally want a propeller to be.

Indeed, the mounting of a conventional propeller or Flo-Torq II equipped prop calls for a propeller nut torque to be 55-foot-pounds or even 100- foot-pounds in the case of some Flo-Torq II kits. The reason why it is so important the nut be tight is to be sure the propeller is seated tightly on the thrust washer and the prop is centered on the propeller shaft. Propeller experts will emphasize the importance of tightening the prop nut to the specified value or above.

In the case of the Flo-Torq III and IV kits, tightening the prop nut compresses the aft adapter (the bronze splined part) against the thrust washer, not the propeller itself. This is contrary to all advice given before, yet that is how it is supposed to be, indeed needs to be, and here is why:

The Flo-Torq III and IV hub kits have a two-piece hub insert, (one half fixed vis-a-vis the prop, one half fixed vis-a-vis the propeller shaft) that is connected via titanium rod that act as springs. This allows some limited amount of torsional movement between the propeller and the propeller shaft and acts as a cushion when shifting into gear and as a damper at slow speed when the power pulses from the cylinders may tend to get out of sync with the rotation of the heavy propeller.

In order for there to be movement between the propeller shaft and the propeller, the propeller must not be bearing tightly against the thrust washer. If it is torqued down against the thrust washer, it will be fixed relative to it and the propeller shaft.

It took me a while to figure this out. This summer when I put Flo-Torq IV kits on both of my 150's, I noticed the wobble in the propellers. I concluded that something was not right and found the length of the aft adapter did not allow the prop nut to tighten the prop the way I expected it to be. There was a distinct side-to-side wobble which I did not like.

My conclusion was the aft adapter was too long and that if I shortened it a bit that would allow the prop to synch up tight. So I cut about 1/8-inch off the aft adapters and reinstalled. Now the props were tight with no wobble.

The result? My propellers shifted with the same amount of clunk, not the soft shifting I had experienced with my first trial of the Flo-Torq IV kit. I had defeated the design of the Flo-Torq IV kit with my modification, the same modification sosmerc describes above.

Yes, in theory you could shorten the aft adapter exactly the right amount to allow the aft adapter to synch up tight at precisely the point where all slop is removed from the propeller-to-shaft fit, but this is not realistic.

I also caution you that not all propellers, not even all Mercury Flo-Torq props have the same hub length. Adjust one aft adapter to fit perfectly on one Mercury propeller and it is NOT going to fit the next one the same way. This is why there is range in the specification for fore and aft movement in the Flo-Torq III and IV kit instructions.