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Thread: Aligning Engine To Jet Drive
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05-29-2009, 08:54 PM #16
Need to move a big mass of water if that machine is as heavy as it looks. Hamilton 212... yeah, they are a good pump, but you might be a little light on hp with the 305 to drive it. I'd likely opt for something from SDM, better speed (not as good as a Berkley) with good thrust, huge ass ducted reverse bucket like the 212, but come standard with the trim nozzle so you can still trim the boat... and throw that wall of water...
My 2c
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06-01-2009, 11:36 AM #17Junior Member
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Its not as heavy as it looks, it actually got up and went with a 90hp inline 6. It has a really flat bottom and doesn't draw much water.
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06-01-2009, 12:26 PM #18
I think we're basing our thoughts/recommendations on a few things.
Firstly you're 21 feet which is towards the "larger" end of the jetboat scale when it comes to length.
It appears in the picture you have between 25% to maybe as much as 100% more freeboard than alot of jetboats
At 10 feet in beam you are substancially over the average jet hull by maybe 2+ feet
Being fibreglass construction and of that vintage its safe to say thats just physically "alot of boat" and its probably heavy compared to most jets powered by a Berkely style mixed flow pump. Aluminum hulls are far lighter and the presense of what appears to be a cuddy cabin in yours also adds weight which most jet boats wont have
In my previous job probably 90% of the boats over 20 feet with beams aproaching 102" all received axial flow style pumps regardless of motor size.
Im not sure how much you know about Berks yet but basically the impellers are 'cut down' from the largest size to be compatable with lower HP engines. I.e a cut down AA is an A, which is cut down to make a B etc etc Smaller impeller sizes require less HP to spin at a given RPM
A small block powered boat will require a smaller impeller (maybe a B or even C) to spin effectivly with the power of a 305. However that means its inherrently less efficient than an AA impeller(youve basically cut away portions of what moves the water) especially when it comes to moving more weight.
Alternatly axial flow pumps, like the Hamilton, work quite well with small blocks and still move a tremendous amount of water. In fact a Hamilton pump with a smaller engine will still move a big boat quite effectively. With an axial pump adding more HP tends to have more effect on planing time and load carrying ability than on top speed. (Hamiltons seem to eventually "hit a wall" in top speed when it comes to adding HP, more power wont increase top end)
Adding more HP to a Berkeley pump will have more effect on top speeds than its ability to plane and carry loads because its only moving half the amount of water at a given rpm. While they usually show gains in top speed when more power is added eventually it becomes difficult to get a big enough impeller to 'hold back the HP'. Racers use "over standard" impellers as big as AAAA, but spin them at 5-6k using over 1000 HP
Sounds like you're on your way already with the Berkeley so its too late but Its not too late to consider power. I may be tempted to consider a big block in a boat that size to allow you to stay with a larger impeller etc
Hope this helps
Cheers
p.s. lets see more pics!"If you ain't hittin bottom.....you ain't jetboatin!"
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06-05-2009, 10:56 AM #19Junior Member
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So I started to tear my engine apart to rebuild the heads and put new gaskets in. The valve cover says mercrusier 305 but after removing the manifolds and valve cover and pulled the heads...its definitely not a 305...its a 350! So it was a nice surprise and I bought this engine real cheap thinking it was a 305.
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06-06-2009, 03:26 PM #20New Member
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I have a 64 Buehler contessa 16' with a 318 Crysler. The boat does not perform like similar set up Buehlers. It is a little slow especially in turns. Engine runs fine,should be enough power. any ideas?
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06-25-2009, 07:26 AM #21Junior Member
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So I have my jet drive mounted and in place. My controls are next to get installed and was wondering about the quicksilver control rod(not sure the part name) that I believe controls the trim of the jetovator. Well the cable to that was cut off by the previous owner probably for quick removal, how do you replace that cable or do you have to replace the whole assembly looks like it does not disconnect. Also anyone have any pictures of how to properly hook it up?
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06-25-2009, 07:36 AM #22Junior Member
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Its the cable system with the spring mechanism.