Hull extention (will it work?)

[CarMan]

Hi i hawe a bayliner 3288
This boat a bit stern hawy when driving (the boat trawels in 10-12 kots) I always travel whid all 4 trimlabels fully down!
I want to extend the hull to get more flotasion on the stern.

The thing whid this boat is thet the propelers are not ounder the boat, th props are in a half tounel. The rouders are montet on the stern outside the hull.

If i extend the hull i need to extend the tunels, i am woryd aboat how it will infekt the manowering of the boat in realy low speed (1-2 kots)

If i do the hull extention only abow the tunels do i get anny help whid lifting upp the stern in speed? (max speed on the boat is 16 knots) Wll it gett anny bad noys or anny thing els bad?

her is som pics
what is the best design?

[CarMan]

Ehen i mowe my boat sidways in a harber i use one enging forward an tha ater i rewers + the rouders fylly tilted, then i use my bow truster.
this maower will use the rouder to wash water from propeler to the midle of ten boat, i i ghot tounels i woryd aboat the sidway trust will be stopt by the tunnel.

[CarMan]

If i do not do the extention as wide as the hull, i do not need to mowe exhouse pipe.
whad bad do a hll extention how isent as wide as the boat do?

som pics of an ater boat whid the same sxtention don (tis boat got the ounder hull, how i do nit ghot!)

[CarMan]

forgoth the pics

[CarMan]

I thinking off doing a "box" then mont it on the boat.
her is a simular "box" to a Bayliner 3870 and a picture off one 3870 whit this "box" montet on the boat

[CarMan]

This was maby a hard questian!
Do not anny one hass a coment at all?

[daiquiri]

I would extend the tunnels also (like in the Bayliner 3870 case) because it avoids creating steps behind the hull. From the hydrodynamic point of view, steps are dicontinuities in the water flow - that means production of strong vortices and drag.
Also, since you have higly loaded props, waterflow velocity is high behind them. That will induce low pressure zone behind such steps. The latter might induce vibrations or even a cavitation which could damage the hull extension or the hull.
So, a smooth extension is adviceable.

[CarMan]

Thenks!
is it ok to extend the tunels like this?

its easy to do it like this. And the rouder are going outside the tunel in full turn.

[daiquiri]

I suggest you to create aeration holes at the points indicated with the red arrow in my attachments. The section view (also attached) explains it better.

Without aeration holes you will have a strong vortex (of recirculating water) in that zone, with a related low pressure area (suction), which will act against the pitch-down effect you want to obtain with this hull extension.
The aeration hole will allow water to leave the trailing edge of the hull bottom, just behind the circular tunnel, smoothly. There will still be a vortex over there, but this time it will be recirculating air. The suction force will be much lower and so will be the drag and the pitch-up moment.
I've put a 1/2" diameter, but if you use 3/4" instead it can only get better.

It is similar to what is usually adopted for stepped planing hulls. In case of high-speed hulls with one or more steps, the air must be allowed to continuously infiltrate behind the steps in order to prevent creation of a water vortex which would induce a strong and sudden drag increase - so strong that it could lead to injuries for people aboard. Not your case, don't worry.

That rudder will be working in a strange environment, actually... I can't tell you how will it's characteristics be modified. You'll have to try and see.

[CarMan]

Thenks!

[CarMan]

Here is som pics of my boat. this is how it looks today.
Is the props anof ounder the hull to get tis to wor well?