QSC 600hp or QSM 11 715hp (dry turbo) same boat

[Thomas Riley]

Hi Tony
I plan to buy a Back Cove 41 and have the option of either the QSC 600hp or the QSM11 715hp dry turbo. I’ve read opinions on both in this approximately 15 ton planing boat with some saying the QSC is under powered and others saying the QSM has heat related problems to to the turbo/manifold if the extra horse power is actually used. Assuming the boat is correctly propped and Predominantly run at say 80% or less than max rated RPM, which motor would you pick??

Topic

[Steve Lewis]

One more thing……

when looking at THIS boat and THESE engines you can not look at the rated HP as a determinant. You have to look at real world usable cruise power and that is 400HP for both engine options. The big difference is that the QSC can run up to rated power for short bursts(1hour for every 8 hours of use as per the published performance curve) where as the QSM will suffer damage to the exhaust manifold when pushed beyond 20GPH @2050-2100. The dry turbo/exhaust is the limit on the QSM and 20GPH is that limit. If you need to get to an anchorage or out run weather you may have more usable top end with the QSC than the QSM. For normal cruise you are probably even up.

Also if you are going to be running in rough water and need to slow down for conditions and run on the edge of hull speed/plane then you may also be in better shape with the QSC.

Plenty to evaluate

[Scotth]

Engine choice aside, is 600-715 hp enough power to do what you want? Doesn’t seem like enough HP for that big of a planing boat. I would like 2X QSC’s, but that is just me:)

[Thomas Riley]

Steve, THANKS!
Not only did you definitively answer my question, you also answered the un asked and more important question of solving the over propping problem of this boat. Much appreciated.

[Steve Lewis]

I thought of the same…….

Thomas,

A while back I asked a similar question that brought me to the following conclusion. The QSC550/600 and the QSM11 have similar cruise RPM burn rates. 20 gallons per hour per engine at max cruise. I am looking at both of the performance curves as published by Back Cove right now. The QSC600 equip’d boat will do ~21kts at 2600rpm burning ~23GPH. The QSM equip’d boat does about the same speed and the same burn but at 2000rpm. Adjust both down a bit as they are over prod’d. Remove some pitch to get the burn down to 20gph and you are still looking at similar cruise speeds. IMHO you are probably better off in the long term with the QSC as it gives you the same cruise speed but at a higher RPM so there are more cooling fluids circulating through the systems.

Larry Backman may be a better opinion as he has a similar boat with the QSM so he has real world experience with the QSM, its performance and maintenance costs. My opinion is theoretical at this point.

Read this and you will see what I asked and what opinions were rendered.

Proper Loading of a QSM11-715

Pay close attention to Corey Schmidt’s response close the end of the thread.

Cheers!

2 users thanked author for this post.

Scotth, Thomas Riley

[Author]

Replies