Weight distribution

Rich_88 · 16 August 2020, 16:04

Hi all,

Maybe someone can give me some advice.

I have a Humber 5.5m fitted with merc 75p opti.

Engine has been on for about 2 months, previously I have a 2001 75hp Marina.

Since fitting the Opti the boat feels as if it is front heavy once up planing. The Opti is a heavier So if anything should feel rear heavy.

What could be causing this?

It feels a bit skittish when I start hitting 25kts.

Thanks
Richard

jeffstevens763@g · 16 August 2020, 17:28

The heavey engine will cause the skittyness you were probably bang on with the previous engine fill a drum of seawater up throw in the bow try that take some out to fine tune then stick that weight in the bow with kit you carry

Rich_88 · 16 August 2020, 18:47

Okay...

I have tried putting my auxiliary up front, at rear, fuel tank is 55L about central under console..Tried full and near empty..

All different scenarios but still feels front heavy.

Could it be engine to high? Low?
It is what is the “correct” height. Cavitation Plate is just Above the bottom of hull.

jeffstevens763@g · 16 August 2020, 19:21

Cav plate should be level with the keel but can be an inch either way having said that different hulls act differently when you said skittish I took it as the bow was light. Trim angle too far in will push the bow down. Easy to sort if you have power trim if not move the trim pin and weight to get the hull level on the plane.your cav plate will be ok at that. I take it the prop is the same as previous

Rich_88 · 16 August 2020, 19:31

Hi

Cab plate is just above level.. 10mm give or take.

Today about 23-25 knots..
Trim out further and further with no effect on lifting the bow, tank quarter full. Two people on board, side by side so center of the boat.

Previously I had trim tabs fitted to help with old engine as it was rear heavy.

It a weird phenomenon.

I though engine too high as I can’t get any effect when trimming it out/up.. I can hear it starting to accurate..

SixtyNorth · 16 August 2020, 20:13

You could try giving Humber a call and get their opinion. They have been building the same hulls for many years so should know of any issues.

jeffstevens763@g · 16 August 2020, 20:29

Sounds like you need the trim tabs but why I don't know. Are you propped correct do you get on the plane quickly or does it struggle. What is your RPM at WOT is it within the sweet RPM range. Might be your borderline on Hp at 75 hp. No water in the hull?.

willk · 16 August 2020, 20:35

Quote:

Originally Posted by Rich_88

Since fitting the Opti the boat feels as if it is front heavy once up planing. The Opti is a heavier So if anything should feel rear heavy.

What could be causing this?d

Might be the prop? Some props generate more "lift" than others...

jeffstevens763@g · 16 August 2020, 20:39

If you needed trim tabs before my guess is under power without knowing all the info on RPM, prop, etc. I had a ribquest 595 m with a 90 Suzuki 4 st 14 x19 Ali prop 40 knots perfect conditions two up full kit 90 ltrs of fuel as a comparison. as sixty north has said a quick call to Humber will sort you out

Orwell boy · 16 August 2020, 21:09

Bit of a strange sounding idea but helped me recently after new engine to my 5.3 ..........
Use a railway sleeper and trolley jack to find the balance point of the set up ,on the trailer will do fine ,providing its a good fit ,when you find that place along the hull thats probhably where you need to be sitting ,if its wrong get your horse feed bucket in the bow and start filling with water with sleeper under in linewith the seats until you find how much weight you need to balance .
just an idea ,some may say rubbish but helped me !