Lift strake modification

Questions about modifying a design

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duke
Posts: 2
Joined: Thu Sep 11, 2014 12:49 pm
Location: NE Scotland

Lift strake modification

Post by duke » Thu Sep 11, 2014 1:59 pm

Hi there

I am building a Catalina express, the plan states lift strakes nearest keel must end 4ft short of transom to prevent cavitation.

If I am installing a system like IPS with 2 props through the hull bottom, what changes need to be made to the lift strakes

Look forward to any advice.

Cyclone
Posts: 63
Joined: Sun Jan 08, 2012 7:26 pm
Location: Barrie, Ontario

Re: Lift strake modification

Post by Cyclone » Mon Sep 15, 2014 2:38 pm

I think the lift strakes will be fine as originally designed. I think the bigger problem is how to incorporate an IPS drive into a hull design that was not designed for it originally. Not to say that it cannot be done, since you are building the boat it might be possible. I have heard that retrofitting an IPS drive to an existing boat that originally had another form of inboard power is not really feasible. You would have to get the design specs for the hull opening and drive mounting and incorporate them into the hull. I would think it might be easier to put twin IPS drives in an existing Vee hull design as there would be one drive coming through the bottom of the hull on either side of the keel where the hull surface is relatively flat. Not sure if the Catalina design would take the weight of a twin drive, probably not. A single drive would have to go through the center of the vee and depending on the requirements for the hull shape to accommodate the drive, might you need to incorporate a large flat spot on the Vee where the drive comes through. If this was required it would involve very significant design changes considering the keel area is the back bone of most boat designs. To understand what would be required it might be best to contact the IPS manufacturer, or look at the design of a new Vee hull that was designed to use a single IPS from the start. I am not sure what different configurations in IPS drives are available at this time and if there is one that might be more suitable. Just my initial thoughts on this.

duke
Posts: 2
Joined: Thu Sep 11, 2014 12:49 pm
Location: NE Scotland

Re: Lift strake modification

Post by duke » Wed Sep 24, 2014 1:13 am

Hi there

I agree 100% with what you say. To be more specific in what I intend to do, have a look at http://www.glen-l.com/designs/special/e ... drive.html

I don't want to bore a hole through the keel and weaken the boat, hence the fitting of 2 props.

The electric motors will be substituted with 2 @ 90° gearboxes with shafts running to a single 1 in 2 out gearbox, to be driven by a single Ford diesel engine.

Prior the development of a 360° steering system, a normal marine gearbox could be used. System would then work as a conventional drive, albeit with 2 props and 1 engine.

If the 2 units could be controlled independently, and i realise it is a big if, along with a bow thruster I think a good degree of manoeuvrability could be achieved. I think the bow thruster would still be required due to the 2 units being driven by 1 engine, even if they steered independently a different power level could not be applied.

Reasons behind this idea include, the boat will mainly be used on a canal, it will be launched from a trailer and therefore the props being set higher up the vee are less likely to be damaged, this will require less maintenance than a sterndrive and could be done substantiality cheaper.
I am a woodworker to trade, I have a son who is a mechanical design engineer and another who is studying electronic and electrical engineering and we all love a challenge! As with all youngsters nowadays both are computer whizzkids.

How well the system works will of course be trial and error as none of us are marine engineers.

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