Qsb 5.9 480 Recon

[keoki93]

I run a 38’ buddy Davis with twin qsb 5.9 480 Recons.

 

previous motors were Detroit 671s then previous owner repowered with the qsb’s. Every since repower there has been bad vibration at 1400-1800 rpms with the right props which were 24×24 4 blade Veems. When I first got the boat we hauled out for a dry dock and noticed the shafts were hard to spin then we noticed wear on both rear cutlass bearrings which were changed. Then we figured out that the shafts were bent and old so I ordered new and installed.

The previous owner over propped which were 24×28 to get more speed with less rpms so it wasn’t noticeable at trolling speed however the STBD motor does shake at that speed.  This has been an issue I have yet to figure out and I want to crack this. I have gotten 24×22 from treasure coast propellers and am about to haul out to change them. If it still vibrates at that same rpm range with three different prop sets what should I do? 

aloha 🤙🏽

Topic

[Tony Athens]

You are totaling missing the point..

1. It does not matter anymore what your boat actually weights.. It is what is is and you have to work with that

     2. You are not addressing my questions regardless of what you think

[keoki93]

Well I’m out of luck, there’s no way to weigh the boat I guess. There’s no scale on out travel lift, I haul out on the 4th I can see what I can do 

[Gene Fuller]

Gross and Net tonnage are measures of volume inside the hull, not actual weight. Those numbers are used for documentation.

As a example, our 37 foot trawler has dimensions of 19 GRT and 15 NRT. It weighs about 25,000 pounds hanging in the Travel Lift slings.

1 user thanked author for this post.

Tony Athens

[keoki93]

Sorry I did reply early if you missed it.

Gross tonnage is 40 and Net tonnage 24.

[Tony Athens]

Quid  Pro Quo

Properly answer my earlier 7 and I’ll take the time to explain my reasoning.. 

 

[keoki93]

So do I have the wrong transmissions for these motors? Howcome the 2:5 instead of 2:1?

[Tony Athens]

It will help but IMO, not enough.. We’ll see.. Specs you gave him should have been 472 BHP @ 3465 RPM

 

 

[keoki93]

And this is the only way from trying to figure it out so you are being a big help

[keoki93]

This is the rpm and fuel burn sheet

[keoki93]

Correction on the weight it is 30 GRT.

not sure where the motors came from as well. And the tacos are Mercury displays of that’s what you mean. I am definitely over propped because I get a lot of blow by coming out of the intake breather before the airseps on both sides. <br /><br />I can get pictures tomorrow when I am at the boat for you. And can I also ask why the 2.5 gear ratio? I just ordered new props from Treasure coast customs and told them I wasn’t getting the full rpm and gave them all my specs weight rpm WOT everything and they sent me 24×22 props.

[Tony Athens]

1) If your tach is accurate, you are getting full throttle advance, then your engines are so over propped that they are being Strangled to a slow but for sure death. Have your tach been checked for accuracy? NO LOAD in neutral should be 3470 RPM or so. Do you get that?

2) Who is guiding you this this endeavor as to trying to sort this out?

3) On the surface, you need new gears with a 2.5 ratio gear ratio for starters.

4) Any idea where th engines came from?

5) How about good pictures from all around show all–Lets see if these are Factory QSB 480’s or maybe something else.

6) What exact instrumentation do you have? This is super important with an engine like this?

7) Also, your weight, 48 tons? Maybe 48000 lbs and that would be hard to believe either

 

I want 7 answers or comments.    

[keoki93]

WOT 2750 RPM 21 -22 knots

Cruise RPM 2500 80% load 16-18 kts

Vessel weight 48 tons

[Tony Athens]

What is your WOT RPM and speed?  Cruise RPM and vessel speed?  Approx weigh of the vessel?

[keoki93]

ZF 280 2:1 gear ratio

[Tony Athens]

What exact gears and gear ratio?

[keoki93]

Alignment was good in the water after a week they done it again and it was good once everything was settled. I just don’t know what else it could be and why is it doing the same thing with two different set of props? 

[Woo]

How is the alignment? I presume someone’s done it, but has it been done really well? If everything is straight, the resilient mounts okay, and the props are “good”…….

[Author]

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