Possible 410 DA Purchase

[Alex F]

.....At this very moment, I am about 200 rpm low.

When we went in this Spring we were making 4600, with all the crap on the boat, fully loaded, which is rated WOT for these 370 hp engines......

This sounds like a great news. If at the very beginnig of the season your boat performed to the specs (engines and underwater gear tuned) and clean bottom, then it you know that you achieved optimum performance for your application. But, currently you're overloading your engines.

I'm sure you're on top of the things, but I would just focus on "what has changed between spring and now?". As you know, this is very common situation to have change like that at the end of the season due to some slight marine growth on the bottom or the running gear. If you know that nothing changed with your props (no damages due to hitting something or grounding), then I would think that marine growth is the primary contributor. Even if you have diver cleanning the bottom I can't say that you can count on 100% results. The test time has to be timed correctly. For example, if your diver cleans the bottom on the 1st of every month, then at the end of each month you obviously have good level of growth, if you're not using the boat every weekend.

There could be other variables, but one thing I know based on personal experience is that when all compenets remain unchanged the boat performs the same or very close to the same at the end of the season as it did at the beginning. I tuned my props on my 320DA and then didn't touch them for 2 seasons. I always do performance test at the beginning and end of the season (just like you, with full fuel, at least 1/2 water and gear). My boat always produced the same numbers.

Having said that I think there's some variable in the picture that has changed and I hope it's just some marine growth, as it's the easiest to fix.

BTW, last year I happen to test drive one diesel 400DB from your area at this time of the year and the boat hardly plane, but it barelly spun those props at WOT. The 2600RPMs rated engines barelly turned 1500+ RPMs and couldn't even trigger the turbos. The cause of the issue was a month old marine growth.

 

[osd9]

In the spirit of 'let's fix Rick's boat'....a few observations.

-According to Mercury Marine, the specs call for a 'range' of WOT RPMs for the 370 HP 8.1 motor. Rick's WOT, as of his 10/2/11 test runs, is within the 'range'.

-According to the Sea Ray reported performance specs, that Rick posted above, for the 2003 410DA with 8.1 gas motors , Rick is making less WOT RPMs then the test boat, going slower at 3250 RPMs then the test boat, and, most likely, running MUCH heavier then the test boat.

-Generally, when you are overpropped, you will go FASTER at a typical cruise RPM then if the boat were correctly or underpropped. Rick is seeing just the opposite.

My guess would be that Rick has a dirty bottom (aka:not lilly white) and/or fouled props/running gear which are contributing to his lack of speed performance.

Prop geometry is very immportant. If it turns out that the bottom and running gear are pristine, then it's off to the prop shop.....

 

[copb8tx]

I am very interested in hearing the results of Rick's prop tuning. I believe our boats are essentially the same so it’ll should be a great benchmark for me.

 

[HUMPH]

Dom,

I will be having the valve adjustment very soon as it is due and I don't know if the PO ever had it done. I am at 280 hours so I should have had this done earlier this year. My bottom is super clean since I am in fresh water and run the boat at least every 2 to 3 weeks and spent 2-weeks in salt water a couple of months ago. I imagine I should have the CAT tech adjust the valves then run the boat and have him verify the RPM's to get accurate data then I will have the prop scan done.

BTW, what speed do you get at WOT?

 

[fwebster]

Ken,

The service work you want to have done is "reset the engine overheads". On A Caterpillar engine with unit injection, that includes resetting the valve clearance and resetting the injectors. Since both the valves and injectors are cam operated on these engines, resetting the overheads resets how far the valves and injectors open as well as when on the cam rotation that happens.

As valves wear in, they sink a little further into the head and that reduces the valve lash or clearance. With less clearance, that means your valves are opening sooner and further than factory specs call for. Don't put this one off.........less clearance means your valves are getting closer to the pistons that they should and we don't want to read about another valve failure on 3116/3126 engines.

Typically, the valve adjustment isn't going to appreciably affect rpms. It will affect engine noise, smoothness and efficiency. To change rpms in a meaningful way you are back to prop dia/pitch, blade cup, load on the boat and bottom condition.

 

[HUMPH]

Thanks Frank, I'll call my guy at CAT on Monday and arrange this service. I want to verify all is running properly prior to any prop scan. I will need that done to optimize my performance though.

 

[mistercomputerman]

The runs I posted were after the boat sitting about 30 days in September/October after doing a short haul for a power wash on the bottom. So, the 200 rpm drop is most likely due to some marine growth on the running gear.

Since I am not going to unload the weight from the boat (although carrying an extra ton of water and fuel around does have me thinking) it's off to the prop shop for some cup.

I blasted the bottom a couple of years ago and did the Interlux barrier coat with ablative bottom paint, so the bottom is pretty clean and smooth.

 

[HUMPH]

The runs I posted were after the boat sitting about 30 days in September/October after doing a short haul for a power wash on the bottom. So, the 200 rpm drop is most likely due to some marine growth on the running gear.

Since I am not going to unload the weight from the boat (although carrying an extra ton of water and fuel around does have me thinking) it's off to the prop shop for some cup.

I blasted the bottom a couple of years ago and did the Interlux barrier coat with ablative bottom paint, so the bottom is pretty clean and smooth.

How often do you have to bottom paint in your area?

 

[mistercomputerman]

I redid the bottom 4 years ago and put a coat of ablative on every year for the first three years. I did not put any on last year, except for touching up the edges.

The bottom is in excellent condition, growth is minimal. The running gear and prop is the only thing that ever gets any junk growing on it.

 

[MasterFab]

Frank,

I have a question. You stated in post #45 that:

"As valves wear in, they sink a little further into the head and that reduces the valve lash or clearance. With less clearance, that means your valves are opening sooner and further than factory specs call for. Don't put this one off.........less clearance means your valves are getting closer to the pistons that they should and we don't want to read about another valve failure on 3116/3126 engines"

I would agree with the first part of this statement, in that, as the valve seats wear, the valves do sink into the head, and the valve lash is reduced. I would also agree that this increases the effective duration of the camshaft, so the valves do open and close sooner and later, respectively. The overall valve lift is also increased, due to the reduction in lash. However, the ultimate, maximum lift point of the valve remains unchanged, so the piston-to-valve clearance remains unchanged. The seat position has changed, the lash has changed, but not the valve position once the lash has been removed, and the follower is riding the cam lobe.
When the valves are re-adjusted to compensate for the valve seat recession, the piston-to-valve clearance will be increased from the original value, but valve seat recession can never be the cause of decreased piston-to-valve clearance.

Having said that, in no way would I put off this scheduled maintenance, either. The effective increase in cam duration can result in rough idle, reduced low-end torque, and reduce low speed efficiency. The valves are also effectively seated for less time during the combustion cycle, and that could have a detrimental long term effect on the valves and valve seats, since the valves, especially the exhaust valves, are cooled during the contact time with the cylinder head.

Dale