knottyBuoyz III The TW28 Project

[laporter]

Ok guys, I've had the plans for almost a full week. Time to start asking some dumb questions.

Material recommendation for prop shaft. Considering boat will be used exclusively in fresh water will a steel shaft, propulsion & rudder stock, properly coated, be viable? Cost is about 1/3 that of a duplex stainless shaft such as Aquamet.

Termination of shaft log. Is a stern bearing (see picture below) required or can the stern tube be machined to accept a non-metalic cutlass bearing? The plans just show a simple flange holding what looks like the shaft log.



I'm sure I'll have a boatload (forgive me, couldn't resist that one) of questions as I go through the planning stage, but I'm prone to working out all the details of a project to the 'nth. degree. Please bear with me. So far it looks like a Spring 2008 start, that's when the building structure becomes available. Till then, planning, strategizing and acquiring stuff.

Thanks.

Rick

[dewers]

Good luck on your quest, I am sure some (me, if my better half does not put me under) of will repeat this. We want a weekly report on yuor progress

Good Luck again

Dave

[jacquesmm]

Your plans include an expanded version of this HowTo file:
http://bateau2.com/content/view/132/28/
It shows all the components of the drive train.

The stern bearing is what 99% of boats use. It is not impossible to do what you describe but why?
If you have a problem with the stern bearing, it can easily be repaired with the stern bearing, not with your system.
Imagine you grab a net in the prop, bend the shaft. How are you going to get it out with your system? Cut the keel?
BTW, your picture is a classic stern bearing bolted to the keel.

The shaft material used in my calculations is Aquamet SS. Cheaper metal will not take the torque.

[laporter]

http://bateau2.com/content/view/132/28/

Page won't display.

It is not impossible to do what you describe but why?

I've seen it done that way a few times.

Aquamet SS

17? 18? 19? 22?

How are you going to get it out with your system?

I would assume that if I had grabbed a net I'd have bigger problems than just a bent shaft. I think it'd be the same procedure to pull a bent shaft from either arrangement. No stern bearing would definitely mean wiping out the cutlass bearing at least. It looks like somebody's pulled all of Macca's photos so I can't refer to them but it looked like he didn't use a stern bearing. It's hard to tell from this angle because of the screw but it doesn't look like there's a stern bearing there unless he's totally encapsulated it in glass & resin.

[Toni V]

http://bateau2.com/content/view/132/28/

Page won't display.

Just wanted to say; works for me okay.

But Macca's tw28 seems to be missing?

[jacquesmm]

- Aquamet 18.
- the page works
- net or line around prop is now big deal with AquaDrive and we show that on the plans.
- if you really want to change things, do it. It's your boat but you asked for my opinion and I gave it.

[laporter]

- Aquamet 18.

Thanks

the page works.

For some odd reason I can't get that page to load. Lost in cyberspace I guess.

net or line around prop is now big deal with AquaDrive and we show that on the plans.

Acknowledged and understood.

if you really want to change things, do it. It's your boat but you asked for my opinion and I gave it.

Well there's no doubt I'll change things to suit my requirements but you are the designer and I value your insight and approval. We're all trying to learn here and the open exchange of information can only benefit your clients as they seek to accomplish their projects in the most cost effective and efficient manner. As we all know mistakes and poor planning with boat projects can cost dearly. I only want to plan and execute this project properly and if there's no need to spend $400 on a stern bearing then I'd appreciate a recommendation for a viable alternative and to not be summarily dismissed.

Please understand that this project represents a considerable capital investment on my part, which is rapidly approaching $50K US. So you can see that there are certain risks I'd like to mitigate if possible and if I can rely no your's and your clients experience with similar projects to find economies I'll be able to do that.

[jacquesmm]

I understand all that and that's why the plans are so detailed.
Many other plans don't show such details.
I know that in some old wooden boats, stern tubes were custom made and some had the cutlass bearing in them. I have not seen that set up very often and I saw and designed many drive train installations. I would say more than one thousand total.
In the late 80's, I made a living subcontracting inboard engine installation, design and engineering to major boat manufacturers and retrofitters.
I hope this gives you confidence in my design choices: the plans are for amateurs but the designer is a professional.
That stern bearing will always cost less than a custom made stern tube with integral bearing housing.
The stern bearing housing we show cost around $ 80.00 in that size.

I do not want to summary dismiss changes but I did spend a few days writing that file about engine installation and most questions are answered there.
Please try again to see it.
Start at
http://bateau2.com
go to "HowTo" then to "Building methods" then at the bottom select "engine installation".

It is a little early to discuss drive train details anyway.

[laporter]

I understand all that and that's why the plans are so detailed. Many other plans don't show such details.

Yes I've noticed that and I appreciate the effort.

I know that in some old wooden boats, stern tubes were custom made and some had the cutlass bearing in them.

Maybe it's a freshwater cheapo way of doing it. If you don't recommend it I won't do it.

In the late 80's, I made a living subcontracting inboard engine installation, design and engineering to major boat manufacturers and retrofitters. I hope this gives you confidence in my design choices: the plans are for amateurs but the designer is a professional.

Absolutely, no argument there. I also have a background in Marine Engineering & Logistics and specialized in all aspects of supporting a large fleet of modern icebreakers and buoytenders so you could say I am a professional in the trade just not an amateur builder. Maybe this explains some of my obsession with attention to detail. The "Devil is in the Details" right?

The stern bearing housing we show cost around $ 80.00 in that size.

I haven't found one anywhere near $80 but maybe I'm looking in the wrong place. Included is a snapshot of the spreadsheet where I've got the estimate for the running & steering gear.

It is a little early to discuss drive train details anyway.

This just happens to be where I'm at in the planning process. When I'm finished I'll know, to within 2% - 3% of what the final cost to complete the boat will be. It's that logistics background I think.

Anyhow Jacques, I appreciate your time and value your feedback. If I ask stupid questions it's because I've stumbled across an inconsistancy somewhere and they may not be in your drawings or plans but with some other source I've read so bear with me. The only stupid question is the one that doesn't get asked, right?

Rick

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[jacquesmm]

Whow, we have to give you a competitive quote when you get closer to install the engine. That is very expensive.
For example, the shaft coupling should cost $ 65.00, not 255.00. Unless that's a flex coupling. Same for many other items.
You have do some comparison shopping.
The cutlass bearing, list price here is 85.00, you show 135.00. The rudder port is $ 78.00, not 105.