Declining Efficiency

quote:
Originally posted by samuel

Something is wrong I say you have the wrong prop. Dealer or someone switch them on you, your wot should be 5200 rpm I thing this link will help you it is your motors and boat.Oh by the way I assume when your riding you have your trim tabs up and your out drives trims properly.http://www.boattest.com/boats/boat_video.aspx?ID=1394

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Thanks for the link and while I can;t say I alway have them trimmed perfectly, I do trim the outdrives to maximize speed all the time and I can't recall the last time I used the tabs - the boat just doesn't need them.

I'm going from memory here but those numbers are not that off from what I used to experience (although I think the top RPM I ever allowed was about 4900 and I specifically recall doing about 36k/41MPH about 2 seasons ago while heading to NJ - it was very calm that day).

The props arent off the hook yet but I try everything that doesn't require a haul and missed boating days first. Although I might jump in this weekend and polish them a little with some really fine steel wool.
 
This is sure getting exciting. The answer is gonna make some people puff out pretty good eh?
 
quote:
Originally posted by jeff_c

quote:
Originally posted by Ghost

You are in a precarious position. I'd get back to blaming the props ASAP, regardless. Don't wait. Scary scary scary.

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I'm not sure what you mean by this. What do you believe can occur? I confirm with my mechanic that he, at least, carefully inspected the props before re-installation and he said he had and there was no deviation from original that he could detect. I did inspect them over the winter too and they looked fine to me. As far as I know they've hit anything other than a little sand (we have a soft bottom where I boat - shallow but soft).

BTW, now I see what my mechanic meant by he is surprised that the one engine was running at all. There was a missing piece of conductor (the little flexible tab that takes the spark from the center spin) so the spark had to jump about 1/2" to make it to the rod that actually transfers the spark to the outer edge of the cap. Oy.

The plug look ok. used but ok.

1 hr run to NJ tomorrow so that will be a good test.

Jeff

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sorry the humor did not come through. If I was in your shoes, my wife would be beating up different shades of purple by now.
 
"Thanks for the link and while I can;t say I alway have them trimmed perfectly, I do trim the outdrives to maximize speed all the time and I can't recall the last time I used the tabs - the boat just doesn't need them."

Since you mention that,... "generally speaking", keeping the outdrives' thrust directed directly aft , no up or down while using the tabs to control attitude is a MUCH more efficient way to achieve max NMPG. But you certainly know your boat better than anyone else.
 
rb2@gr5tghost. LOL. I can't believe I missed that. And, so true. I had the conversation and it wasn't pretty.

So here's an update....the tuneup was done and during my 15 minute trial period I ran the boat up to about 40 mph at 4300-4400rpm and all felt 'right'. I'm not sure if the tune-up is the end all be all on this but the boat definitely needed it...especially with that one bad rotor. I'll get more info here once I've used the boat and get a fill up.

Now the new fun begins...apparently Mercury (and Sierra since they use the same factory) had had a bad lot of caps out in distribution since last year and these bad 'spider' caps were put in boats all winter and they've been failing left and right all spring. Mercury's statement when we called yesterday..."I guess we should have released a service bulletin, huh?" Guess who got two bad caps and ran at 5-6 mph for over 3 hours in the ocean yesterday? But I guess that is going to be a new thread because I am off to a GM dealer to get new caps, as recommended by Mercury, because they say that is the only place to get caps that don't have the casting defect.

Fun stuff this boating.
 
It's not "right" at 4400 if that was all you could wind out of her. You need to be pulling 5000 to 5200 on those engines. You are overloading them.

I'm thinking wrong props/damaged props.
 
quote:
Originally posted by jeff_c

I always thought H20 was 8lbs/gal but in any case I went to the boat tonight and the anchor locker has absolutely nothing in it (except 200' of chain rode) and is mush drier and cleaner than I could imagine. I also check the bilge area under the v-berth (where the bow thruster is installed) and it's as clean as can be...as in it's never had water in there.

The big (initial) test will be performance tomorrow with new plugs, caps and rotors. I can only hope for some improvement.

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Actually it is over 8 pounds: 8.35 pounds approximately. It will vary with temperature and pressure.

George
 
quote:
Originally posted by KiDa

It's not "right" at 4400 if that was all you could wind out of her. You need to be pulling 5000 to 5200 on those engines. You are overloading them.

I'm thinking wrong props/damaged props.

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You are correct. I just got off the phone with customer service at Formula and I will need to confirm that I have 24 pitch props and that the throttle is allow for 100% travel. If it's not that I need to check for prop damage (as been noted here a few times).

This was all I could get out of her:
topspeed.jpg
 
those rpms are very close was the sync on??
 
Thats a smartcraft display.

I dont have a sync engines option. Thats both throttles firewalled with some engine trim thrown in.
 
If you are overpropped (possibly significantly here), then any performance lost will be magnified greatly.

Do you know what the WOT rpm's were when it was new?

The factory can tell you what prop was put on there originally, but that is not the same thing as saying what the proper prop should be. Weight varies from boat to boat and factories tend to prop to barely hit WOT rpm's with an empty boat to maximize the boat statistics. It's a bad practice because it just about guarantees that your boat will be overpropped by 2-400 rpm and costs you a prop pitch change. As others noted, you NEED to be able to hit and preferrably exceed your rated WOT rpm.
 
if that is accurate rpm then both props seem to be performing similarly. That leads me to think they are not damaged. Over propped yes, but I would expect dinged props to result in different RPMs.
Try to find some non ethanol gas and see what happens.
When it is hauled have them weight it.
 
Unless somebody swapped props with him, the condition has chaned over time, which I think leads us back to Weight/Balance.
 
I had a 31Pc, bought it from a guy that ran in on Lake Superior, which is cold and clean so it never had bottom paint. I bought mid-season, ran it with out paint and my top end went from 50mph to 45 by the end of the season. The next year I painted with a Petit hard ablative and was running about 47 at WOT. A soft ablative will slough off at speeds approaching 40, which allows for marine growth. If I read correctly, you said there are many bare spots on your hull without paint. I wouldn't be surprised that growth, which can be nasty within a week, would be slowing you down and hurting your economy.
 
quote:
Originally posted by TIMEOUT90

I had a 31Pc, bought it from a guy that ran in on Lake Superior, which is cold and clean so it never had bottom paint. I bought mid-season, ran it with out paint and my top end went from 50mph to 45 by the end of the season. The next year I painted with a Petit hard ablative and was running about 47 at WOT. A soft ablative will slough off at speeds approaching 40, which allows for marine growth. If I read correctly, you said there are many bare spots on your hull without paint. I wouldn't be surprised that growth, which can be nasty within a week, would be slowing you down and hurting your economy.

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A review of the bottom of my boat will most likely wait until the end of the season and it very possible that as time has gone on it has gotten rougher which would contribute to the situation. However, to clarify my earlier comment...I use ablative and by the end of the season there are areas (aft running surfaces) that have been basically stripped down to the barrier coat but there is no growth evident on the bottom of my boat (it sits in brackish water all week and I use it every weekend so I would assume that contributes to the lack of growth on the bottom).

Also, that would explain a change during the season not the year over yer progression that is irking me.

I'll know more once i've run it for a few hours in my normal conditions With the recent tune-up.
 
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