Running gear design issue.......

The hull appears to have a lot of rocker in it. In my opinion, the tabs are undersize. It's bordering on a Jersey Speed Skiff.

By the way... BEAUTIFUL tender!

Also check for rudder balance and bearing conditions.

nice, ive been searching for something like that for a while.....

ill take it off your hands, no problem

38 knots at WOT is pretty good for that boat and HP combination. I'd like to see a little less pitch and more rpm at full throttle. I'm assuming 4800 rpms is with you in it and no other people (light)? Check your exhaust and make sure there aren't any spots where it is vibrating against the hull. If it has a small tunnel, you might be stuck with the vibration as the tunnel might not have been designed to handle as much waterflow as with the new horsepower. How close is the propellor blades to the hull. If there's an inch or less there, then that could definately cause vibration from what I've seen.

Hi,

Sounds like it could be a weight issue (trim angle). Though having said that, she looks as though she's sitting on her lines nicely.
As Carl said maybe bigger trim tabs, or next time she needs some paint, could add more buoyancy (wide spray chines).
I could run some numbers on the beam and determine a trim angle to suit if needed.

By the way, gorgeous boat! Cheers

Far

Nice Boats! It would be worth the drive down from wilmington.

The vibration and running angle are two different animals. Has the shaft been checked with a dial indicator? You said the cutlass bearing was worn, hopefully the alignment issue was corrected. CNC scanned wheels are not necessarily the end-all, they usually only measure the aft blade faces and differing blade thickness can sneak by undetected. Try and find a shop that will not only do a static balance but also a dynamic spin balance the same as you would a car tire. I know some of that sounds pretty basic but it doesn't take much to cause vibration at those shaft rpm's.

A side pic of the running gear would also be very helpful. Too close prop to rudder clearance can cause blade pulses to be transmitted through the rudder stock. If the prop clearance isn't at least 15% of the blade diameter, in this case just over 2", then I'd suggest adding cup if it doesn't already have some. It may require removing some pitch though since you sound propped right at the edge already and freeing up the engine is always a good thing.

The bow high running angle isn't a suprise with that rocker, actually I'd have almost expected some porposing. Wider and/or longer chord tabs will definitely help bring the bow down and reduce the drag you get running smaller tabs all the way, they start acting like speed breaks.

If she is bow high at all running speeds a small bottom change may be a better idea than new tabs. Adding a wedge to the aft running section is relatively inexpensive and can change running angle with less drag than tabs and still leave you the option of using them when you need to lower the bow and punch through some chop but keeping the bow up in following seas. An old trick to decide if a wedge is in order is to stretch a VERY tight 1/4" piece of line from aft cleats, under the hull just ahead of the transom. Obviously this has to be very tight to stay in place but if it breaks her over, you can haul and add a epoxy/cabosil wedge with very little effort and leave everything else as is.

A different design wheel can also help the running angle. Wheels can bemade with different blade rake which can lift the stern, effectively lowering the bow.

Absolutely gorgeous boat and looks like she is better than new! Congratulations on an excellent job, you are in the fine-tuning stage now.

Can you move your fuel tank forward?

I think if there was a porpoising problem, moving the tank forward would help. But it seems like there's a heavier weight issue, and thus a lift issue, as it was running X amount (220hp), and now it's running Z amount (330hp). I would suggest longer Stabs... I think this would be the cheapest "experiment" - trial and error.....

Far

I'm wondering if the vibration is due to the increase in HP and engine size. The size and design of the stringers and engine mounts may need to be looked at. Did the stringers get cut down where the engine mounts are located to accommodate the new engine at the time of the engine swap by chance?

If it's running 38 knots WOT, I don't think it's a trim tab or running angle issues. Sounds to me, it could be that the shaft isn't strong enough for the additional HP and flexing (inspect while running at cruise). Or the tunnel doesn't flow enough water for the additional waterflow causing reverberation.......Or could simply be an exhaust hitting somewhere or alignment.....have you checked shaft alignment with the boat in the water? I wouldn't go moving around fuel tanks and such.....unless I was SURE it was a problem.....adding 100lbs in the very bow, should give you an idea of what moving the tank foward a foot would do.

It would seem the 330 and gear train would be heavier engine by several hundred pounds. Some weight moved forward like batteries may help but I'm not sure how aft weight bias would cause a shuddering vibration.

No, the engine is the same block and weight as what was removed......just different HP via bore and stroke and cylinder head style......etc.......it's probably a touch lighter via the use of an aluminum intake manifold etc etc.....

The mufflers are definately transferring some vibration to the boat IMO.......

ddw1668,

Do you know how much the boat weighs before and after the refit, or a general weight of the boat...? Also the previous motor that was in there...? Cheers

Far

The new motor is based off of the same block as the old motor, so the weight should be the same +/- 100 lbs.