Hull modification help

[howser]

I have a 20ft Cathedral hulled boat that used to have an inboard engine with shaft drive.It was then turned into an outboard,but i dont think the prvious owners got a very good job done.I am getting a huge ammount of splashing from the outboard engine and by looking at it whils on plane,it seems that the tunel that was in the hull to give waterflow for the shaft drive should have been filled in,as all it seems to achieve now,is to throw water up against the leg of the outboard,causing loads of drag and even throwing some water over the transom.<br /><br />How would you suggest i go about filling in the tunnel,what materials,and procedure would you use,the hull is fibreglass.<br /><br />The tunnel is about 20 inches long and approx 8 inches deep and approx 10 inches wide.so is quite a big hole to fill in,and whatever i use,i dont want it breaking away and hitting the prop.

 

[Catchem]

Re: Hull modification help

Howser,could you post a pic on this?

 

[hokey1]

Re: Hull modification help

I have an idea what you are trying to describe, one thing is very important, that is the capitation plate is even with the keel of the hull.Also you are not going to be able to fill the space with just a sort of filler, you are going to have to fabricate a filler to take up some of the void such as laminating 4 or 5 2x10s and glueing and srewing them to the hull after the laminated pieces are formed to the shape of the hull. Next resin and matting need to be applied,you should try to do 3 layers,you can achieve this by how much you take off the laminated piece that was installed earlier. Finally to finish this you can buy fiberglass powder that you add directly to the resin mixture,the beauty of this is you can make this mixture as thick as you want. You can add as many layers of this as you need so you can match the features of the hull. You need to do something like this because whatever you use to fill in that area without first taking up some of the space will not hold up

 

[howser]

Re: Hull modification help

I do'nt have a picture at the moment,but i have used my excellent paintshop skills to draw an exact likeness.<br /><br />Thanks for the help so far guys.Im definately going to have to sort this one out as it must be reducing performance by a lot having that volume of water fired like a cannon at the leg of the engine,and probably putting a lot of unnecessary strain on the transom aswell.<br /><br /> http://www.streamload.com/howser/boatproblem1.JPG

 

[snapperbait]

Re: Hull modification help

Howser.. Does the anit-cavitation plate on the engines lower unit sit at or near the same level as the top of the tunnel?<br /><br />Might be worth while to make an attempt at raising the engine first, just keep an eye on the engines water pressure..<br /><br />Or, since i'm partial to inboards , you could fill that area with inboard running gear and a prop, put the engine in the middle like it was designed for..

 

[howser]

Re: Hull modification help

anti-cav plate sits just above the bottom of the tunnel,(ie it would be approx 1" above the bottom of the boat if it were filled in to match the rest of the hull.At the moment nearly every single bit of water that comes through the tunnel hits the engine above the cav plate,and makes a hell of a mess.

 

[ThomWV]

Re: Hull modification help

You need to raise that engine way up. WAY UP. The cavitation plate should not be set where the V of the hull would have met were it not for the tunnel, it needs to be set at where the water level is as it exits the hull.<br /><br />In a very real way your situation isn't much different that that of a boat that used a bracket. Bracketed boats have the engine height set a good bit above the V of the hull they are on. Our boat, with its 30" bracket by Gil, has a cavitation plate that is 4.5" above the very bottom of the hull. I would immagine in your boat that you are going to have to raise it to equal the height of the tunnel. By the way, nothing that you do to fill in that tunnel is going to work well, don't even think about it.<br /><br />Thom

 

[howser]

Re: Hull modification help

The prop already comes out of the water at times due to the choppy conditions,and because the channel of water that shoots out of the tunnel is quite narrow,when i turn hard,the prop wont even be in that channel of water it will be in the flow of water coming off the lower part of the hull.The engine already ventilates badly in turns,im a bit stuck with this one,raising the engine would be by far the easiest option,but i cant see it working for the reasons i just mentioned,and filling the tunnel seems like my only option.

 

[flashback]

Re: Hull modification help

If you really want to do away with the tunnel, you could sand the inside of the tunnel to scuff it up, then temporarily enclose the tunnel with some cheap plywood screwed to the hull, then fill with 2 part hi density foam. allow foam to dry, remove the plywood, fill screw holes and fair the foam to the hull with a sander, then lay some glass over the whole deal, fair it all, and paint.....

 

[JasonJ]

Re: Hull modification help

I don't see a reason why you can't just fill it in, but the repair wil need to be very strong. You could either build if flat to form a pad, or the better option is to build it to continue the deadrise. It would be stronger this way and ride better. Epoxy, biaxial cloth and roving, and a wood/foam core is about the strongest way I can think of to get it done. Good luck with it...

 

[hokey1]

Re: Hull modification help

Howser, nice picture,you really have to make that tunnel go away, if you raise the motor like suggested you will surely burn it up.As it comes up on plain if it can it will lift the water pickup out of the water,further more the capitation plate needs to be even with the keel.!!!!!!!!1

 

[hokey1]

Re: Hull modification help

Howser,what ThomWV is talking about is known as a Sea Drive, it primarily was used on fishing boats but pleasure boats adopted it also, it served two purposes, first it eliminated porpousing (I think that is how you spell it) along with torque steer.In other words it help keeps the bow from raising and falling back into the water in rough sea conditions while under power, secondly it allowed full deck access witin the boat as for you wouldnt have the intrusion of the outboard into the hull and no need for a splash board.The idea of installing that bracket without doing any fabbing on that tunnel would probably work as long as the transom would accept it (strength and dimensions) The only problem now is longer throttle,shift and fuel line and cables and possibly wire harness as for the motor would be about 2ft away from the transom