Hey all...
Last year I started a thread about the poor fuel economy/performance I was getting with my '99 3055 (5.0L). I couldn't get near the top speed or rpms that most other owners were reporting. We talked about all kinds of issues ranging from carbs, to growth on the bottom, to wrong pitch on the props, etc.
I'd like to update everyone that contributed and run a theory past you...
I think I have the engine performance in a pretty good spot. I ditched the Holley 2bbl carbs I bought from I5 (I don't recommend them, and others concur) and rebuilt the original Mercarbs myself with great success. Engines ran great last fall, and this spring they started up and idled as if the boat had been running just a week prior.
Here's what I discovered: The props that are on there now have a pitch of 21. Pretty much everywhere I read about other 3055s, the original props should have been a pitch of 23. Last year some folks suggested I might actually be over-propped and this is why I couldn't reach WOT spec but now I am leaning more towards the carbs being the cause of that problem, especially since almost everything else I've read suggests that the 3055 came with props having 23s.
Also, looking at the bottom of the boat before it goes in the water, it's actually quite smooth. It does have bottom paint on it so it's not as good as it could be for sure, but it's pretty good.
So now I am thinking that the reason I was not reaching the speeds that others are at WOT, and therefore not getting good fuel economy, is because my props are pitched TOO LOW. It's like losing the overdrive in your car...you're fuel economy is going to suffer (top speed would too if we didn't have speed limits). Isn't it?
Also, and this might be significant, last year I had a RIB attached to the swim platform with the arc davits that weighs about 200lbs. When lifting the rib up onto it's davits, the effect on the boat seemed undetectable, but the more I thought about it...having 200lbs hanging that far back on the boat MUST have an effect on the way the boat planes, causing the back to squat down in the water a bit...wouldn't it? Not to mention the air flow issue (rib is up on it's side when mounted, acting like a drag chute!).
Seems ridiculous that I didn't think of this before, but I figured a 12,000lb boat isn't going to notice an extra 200lbs, but when it's THAT far back I'm sure the 200lbs starts to act like much more.
Can anyone support or blow up my theory? (be gentle if you're going to blow it up...I don't profess to be an expert!)
I want to feel like I'm on the right track with the prop theory before I start looking at replacement props. Any prop recommendations from other 3055 owners are welcome as well.
Thanks!
K
Last year I started a thread about the poor fuel economy/performance I was getting with my '99 3055 (5.0L). I couldn't get near the top speed or rpms that most other owners were reporting. We talked about all kinds of issues ranging from carbs, to growth on the bottom, to wrong pitch on the props, etc.
I'd like to update everyone that contributed and run a theory past you...
I think I have the engine performance in a pretty good spot. I ditched the Holley 2bbl carbs I bought from I5 (I don't recommend them, and others concur) and rebuilt the original Mercarbs myself with great success. Engines ran great last fall, and this spring they started up and idled as if the boat had been running just a week prior.
Here's what I discovered: The props that are on there now have a pitch of 21. Pretty much everywhere I read about other 3055s, the original props should have been a pitch of 23. Last year some folks suggested I might actually be over-propped and this is why I couldn't reach WOT spec but now I am leaning more towards the carbs being the cause of that problem, especially since almost everything else I've read suggests that the 3055 came with props having 23s.
Also, looking at the bottom of the boat before it goes in the water, it's actually quite smooth. It does have bottom paint on it so it's not as good as it could be for sure, but it's pretty good.
So now I am thinking that the reason I was not reaching the speeds that others are at WOT, and therefore not getting good fuel economy, is because my props are pitched TOO LOW. It's like losing the overdrive in your car...you're fuel economy is going to suffer (top speed would too if we didn't have speed limits). Isn't it?
Also, and this might be significant, last year I had a RIB attached to the swim platform with the arc davits that weighs about 200lbs. When lifting the rib up onto it's davits, the effect on the boat seemed undetectable, but the more I thought about it...having 200lbs hanging that far back on the boat MUST have an effect on the way the boat planes, causing the back to squat down in the water a bit...wouldn't it? Not to mention the air flow issue (rib is up on it's side when mounted, acting like a drag chute!).
Seems ridiculous that I didn't think of this before, but I figured a 12,000lb boat isn't going to notice an extra 200lbs, but when it's THAT far back I'm sure the 200lbs starts to act like much more.
Can anyone support or blow up my theory? (be gentle if you're going to blow it up...I don't profess to be an expert!)
I want to feel like I'm on the right track with the prop theory before I start looking at replacement props. Any prop recommendations from other 3055 owners are welcome as well.
Thanks!
K
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