Jackplate drag.... maybe.

[gtflash76]

Shot a video of my boat running around 30mph. Had the kids on board so my trim tabs were fully down and taking it easy.
Boat is twin stepped 8m rib
Etec 250ho. Used to run. 71mph all day long at 5000ish rpm

I have added around 100kg of weight, moved console forward 8" and I added 5.5cmc manual jack plate. prop shaft is level with bottom of hull. I have no cooling issues and use a water pressure gauge. Prior to all the changes I did suffer cooling issues at river speed and she was a pig to plane.

Now running 60mph at 4800rpm. But the video looks very messy. I am concerned my jackplate was dragging or is it all the tabs? The pictures show it is quite low in water

New Video needed but ideas in a postcard? Any thoughts appreciated. I am
thinkjng of removing jack plate and going straight onto transom. I only fitted it as one came up cheap and I hoped to find cleaner water for planning speed

https://youtu.be/pY6emu2Z8zw

[olboatman]

Anything that touches the water or that the water touches (spray) causes drag that robs speed. It seams from the video that something is causing a turbulance on that starboard side. Does the port side have clean water coming off the hull?
Gary

[vnemous]

at 5000 your rpms were low for that engine. Would like to have seen a before video but that motor is very deep. JMO

[gtflash76]

Anything that touches the water or that the water touches (spray) causes drag that robs speed. It seams from the video that something is causing a turbulance on that starboard side. Does the port side have clean water coming off the hull?
Gary

Unfortunately i I do not have a before video and on this occasion I was driving and my lovely assistant didn't look port. I need another test run. It does look very disturbed. There are full length spray rails inboard of trim tabs too

[phillnjack]

the tabs should not be down at all once up on the plane and running fast.
that is not the idea of tabs, their main purpose is just to level the boat side to side at a slow cruising speed.

Raise tabs as far up as possible and then try, your losing a lot of speed with the tabs touching water.

[gtflash76]

the tabs should not be down at all once up on the plane and running fast.
that is not the idea of tabs, their main purpose is just to level the boat side to side at a slow cruising speed.

Raise tabs as far up as possible and then try, your losing a lot of speed with the tabs touching water.

hi phill.

Yes i I understand that, but on this occasion I had the kids, the toddler, the missus, and the parents inc my oap mum all on board and sat rear. I kept the tabs down to keep the sharp bow cutting the waves to make the ride gentler for all onboard

Not an ideal engine height test scenario. I will test again with less people. Less tab and more speed

thanks.

[phillnjack]

well no wonder it is not clean at the back, that is about the worse case scenario you could look at..

just place a camera at the back to watch what is going on at 50mph when the boat is not full of people all at the back.

with bow down you will never get a proper clean wake.
what make a boat is this ?
and are those tubes hypalon of heavy duty pvc ?
when empty of people do the tubes touch the water at the stern ?

[gtflash76]

Scorpion rib. Twin stepped Lorne Campbell hull. They are hypalon and no there is quite a gap to water. Only time they really touch the water is heavy cornering or lots of weight on one side. The diesel ones do but not light weight outboard models of this hull

[phillnjack]

I would raise that engine up and also raise the jack plate on the transom.its far too low, needs to come up by around 5 inches.

is this a 20 inch motor on a 25 inch transom though ? if so that would explain the bad cooling at slow river speeds.

[gtflash76]

The new water pump appeared to fix the coping at river speed. However I did simultaneously put it on the plate

transom is 24.5 and engine 20”. Hence the bullet sitting around level with bottom of hull v