Repowering 1990 luhrs 320

[Cesar]

Hello everybody my name is Cesar Correia from Rhode Island i work on alot of diesels i work for an oil company full time servicing everything they have from diesel vans and gas jobs to large freight liners and kenworts. Lots of diagnosing also. That said i will be doing 90 percent of the work to try and keep my bank account in one piece..Originally the boat had twin 454 crusader 350hp models with 1 3/8 shaft. Originally with 454s 350hp model at 3300 3400 rpms i was doing 18 19 knots calm seas 3500 3600rpms about 23 24knots it really came alive up top but the fuel is killing me. I only have 2 100 gallon tanks and my reserve 75to100gallon reserve tank is out of commission gonna have it repaired and both my tanks inspected when I pull 454s also. I just cant go the distance in the water and not have to worry about finding fuel
…. i have 2 6bts 215hp will I be able to achieve these cruising and top speeds with the 215 6bt if the z63 are geared properly and also what is max power i can push without running after coolers? And Will my 1 3/8 shafts hold up to the job the torque numbers are fairly close .thank you so much for your time.

Topic

[Tony Athens]

Ceasar,

You seem to have a great hands-on background in working on engines & equipment, but you are not understanding my responses.

1) The total operating WEIGHT of your finished vessel will be the main factor as to meeting your performance goals vs the HP you have to put into the props.

Have you weighted your vessel and thought about what it will weigh after you are finished with the restoration/repower? Every extra pound you add will reduce your cruise speed and how easily the vessel gets up on plane. You need to understand that

2) You do not want 2″ shafts under a vessel of these dimensions. Either use 1.375 AQ 22 or AQ 19 x 1.5″.. The most efficient props ( 3 or 4 blade modern props from ACME Propellers-look them up on Google) for this vessel will be in the 18-21 ” diameter range and will be pitched to allow the engines to make approx 100 RPM over the minimum rated RPM with these engines..

A well done 31Ft Bertram or 32ft Blackfin the 15000 lb range will easily cruise 20-21 Kt with these engines set up as noted. If your vessel bottom is flatter in the back ( less dead rise) and weights the same, you’ll most likely be faster.

How fast your vessel will travel, will be determined mostly by its final weight loaded as you use it, the condition of the bottom and running gear, the windage of the vessel and the overall set-up of the engine and repower work you perform.. Hopefully in the end, the weight will be under 15000 lbs.

Tony

[Cesar]

What do I have to do to be confident of achieving 20 knot cruise? Bigger shafts to be able to turn more aggressive prop?

[Tony Athens]

It’s going to come down to the total weight of the boat when the dust settles.. With the props you propose to use, I’d say your chances decrease big time…. 5 blade props and 2″ shafts do not belong on this vessel if planing at or above 18-20K’s is your goal.

Just going from a 1.5″ to a 2″ shaft on a boat like this will cost you not less than 1.5K alone…

You should be looking at 1.5:1 gears and high end modern props like those from ACME–Maybe 20 x 22 3B, light cup if you total weight is under 15000 lbs..

Tony

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Cesar

[Cesar]

What are the chances I will be able to achieve a cruising speed of 20knots? With this setup with pitch and blade design adjustments?

[Tony Athens]

1.5:1 gears would be appropriate for 19-20 ” diameter props using 6BT 5.9 210’s.. The pitch / blade design may have to be tweaked depending on the final weight of the vessel.. In a typical & simple Bertram 31, 20 x 20 3B’s work well this these engines and a working weight of 14000 lbs ..

Tony

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Cesar

[Cesar]

My props are 19×20 any help would be appreciated

[Cesar]

I’ve seen this exact boat with 330s but I’d like to know if I can run 210s and get the cruising and top speeds I have now

[Cesar]

Using the crank pulley as a centerline I measured 34 Inches from hull to hatches the 454s look like there on about an 8 degree angle

[Rob Schepis]

Current shafts at 1-3/8 are good but engine room height will be an issue.. Any more “overview” and deck pics ?

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Cesar

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