Is it the weight on the transom that makes Allison not recommend them? Lots of old boats with wooden transoms running them.
It's got NOTHING to do with the structural integrity of the transom. It's all about the leverage & forces at work with a 2.5 vs 3.0. I "double ditto" what Lou said, Darris has MANY reasons why he is VERY ADAMANT about NOT recommending heavier motors on his 20ftrs. LOOK GUYS do you REALLY think Darris has done this because he enjoys being a hardazz? Do you think he WANTS to DELIBERATLELY cost himself sales & money via this position? OF COURSE NOT! The man is simply, first & foremost concerned about CUSTOMER SAFETY even at the expense of sales!!!
For those that haven't read or actually discussed this personally with Darris, here are a few of the top reasons Darris DOESN'T recommend it:
1). The 20ftrs were extensively and essentially designed SOLELY for the lighter motors. Heavier DFI smalllblocks & all of the 3.0s weren't even in the design stages when Darris was developing the 20ftrs in the late80s-early 90s!
2). The extra weight of 500#+ DFI 3.0 vs a 400# 2.5 is primarily ABOVE the mid-section so that extra weight is magnified significantly, ESPECIALLY in lateral directions.
3). Adding onto # 2). Something alot of people either don't realize or overlook, part of the amazing design abilities that Darris has put into his hulls are those of safety factors/considerations! Some examples are the aerodynamics that essentially prevent a blow over, sure you can "trim one over" but if you've ever stood one straight up on the tail at speed then you've "felt/seen" this ability of the hull to suddenly "lose air pressure & then sit back down" (I have as I stood my FULLY loaded xb03 straight up once in the upper 80s & my partner & I thought we were going for a swim but then the hull sat back down) AND THIS CRUCIAL POINT: The angles of the chines & other edges on the bottom of the hull aren't by accident! Darris designed them as such via years of his methodical "R&D". He states that they will hold the water VERY TIGHT for those infamous, seat base & neck straining, multi-G turns... UNTIL they reach his designed in limit at which THEN they will release their grip, the water will "squish" (Darris' actual term) & the hull will then slide atop the water INSTEAD of digging in & inducing a HIGHLY DANGEROUS "barrel roll". THAT is where the weight limit comes from, that "release/squish" may or may NOT happen with heavier motors!
4). Another key but not always discussed reason is the "ratcheting gearcase vs non-ratcheting gearcase". The 2.5 gearcase is a ratcheting case. That being, when the motor is turned off or killed while still in gear, the prop can still rotate via the water pressure turning it. Everyone's experienced this when their boats still moving at idle speed & they killed the motor while in gear. The boats forward momentem still pushes the boat & a "CLICK CLICK CLICK CLICK" is heard from the motor until the boat essentially stops. For whatever reasons, Merc didn't put that feature on the 3.0 gearcases. So when you kill the power while in gear on a 3.0 the prop comes to a halt as well! No problem at low speed but at high speed, a power failure will STOP that prop which then becomes a multi-bladed rudder which will likely then ASSIST/CONTRIBUTE to the above mentioned barrel roll! :cuss
As I said, it's Darris' primary concern for OUR safety 1st! If anyone doesn't think Darris & Nancy aren't concerned for their customers safety, they DONT know those 2!!!
Yes, 3.0s CAN be built with aftermarket parts like a 15" mid & a 2.5 ratcheting case conversion for 3.0s that "should" make the marriage considerably safer. But GET OUT YO CHECKBOOK for such engine builds! :shock:
And finally, heck ProMax & 2.5 stuff is FINALLY getting ALOT cheaper now as the "new normal economy" & the market itself heads toward newer technologies... You can build LAKE POUNDING engines for half or even less than what it would've cost just 2 or more years ago!
