Testing Design Limits?

[widowmaker]

Is there any mechanical benefit to pushing the boat/engine to top speed/rpm every now and then if the conditions are right? With today's fuel injection systems and computer controls I'm not sure.

With the older style carb engines my Dad would "blow the cobwebs out". I try to open it up once per outing if I can to verify everything's working right. My slip mate never opens his up and says it will wear it out sooner.

Any thoughts?

 

[Dave S]

I see no harm in "opening it up" once in a while. It will tell you if your top end is still attainable because if it isn't it may mean that something needs attention. For example, maybe your hull or outdrive has picked up a lot of growth and needs cleaning. The extra drag can affect your fuel mileage at any speed with this condition and means that your engine will be working a lot harder just to maintain a normal cruising speed.

When I open mine up, it's normally only for a short period of time such as for five minutes or so. If you run at top end all the time, you will definitely be shortening the life of the engine and for that matter all the components in the drive system. You will also be using an awfull lot of fuel as well and at today's prices, thats not too good. :smt021

The best practice for long engine life is to find the "sweet spot" where your engine is pushing your boat along at a good clip and getting a decent burn rate (GPH) as well. If you have Smartcraft, determining the sweet spot is pretty easy. If you dont have Smartcraft, I find that "seat of the pants" :grin: works pretty well too. My 240SD cruised real nice at 3000 RPM.....all that measured by "seat of the pants". On my 260DA, the optimum burn rate for a decent cruising speed is achieved at 3500 RPM but the boat "feels" better at 4000.:huh:

So if you are now totally confused, I'll let someone else take a crack at an explanation. :grin:

 

[sbw1]

I attended a Crusader engine maintenance seminar this summer and the instructor said you should check your wide open throttle 3-4 times per year. It should be done for short periods of say 30-40 seconds. His reason for suggesting this was to make sure you know how you are loading the engines. As you know, the maximum sustained WOT for cruising should be approximately 75% of WOT. (some say 80% for EFI engines). You should make sure you turn the recommended WOT at the beginning of the season so you know what 75% actually is. Checking once a month allows you to take into consideration how WOT changes as the bottom picks up water weight, slime, the boat gets loaded with equipment, etc. Proper loading is still 75% so you might be at proper cruise with 3550 in the spring with a clean, light boat and 3250 at the end of the season. Running high RPMs is generally wastefull and hard on motors and hulls. Have you ever noticed that some people seem to have more than their fair share of motor problems and stress cracks? I see people flying by our dock every week end going airborn over wakes. They really pay the price for operating in this manner.

 

[WFYB]

I believe what the others have told you is correct. You want to confirm that the boat can achieve WOT or a bit more, (with normal operating temperature etc), to confirm that your boat is:
a. Propped correctly
b. Bottom is clean
c. Engine(s) are operating as expected.
Anything less then WOT with a normal load of water, fuel and people suggest that your engines are loaded beyond the manufacturers specifications. www.boatdiesel.com has allot of information on this very subject.

 

[widowmaker]

Thanks for the input. This builds the case for explaining to the Admiral that this is a necessary task from time to time. :thumbsup: I'm not a speed freak but it does sound good when that engine opens up. She doesn't like to go over 20 mph and has been admiring pontoon boats ughhh...