A Few Questions - Page 3

larby · 09-12-2010, 07:59 PM

To be honest, I'd love to reply but don't want to risk being out of my depth and getting something wrong. Personally I'd make it as close to original spec as possible, any weight loss probably wouldn't be worth it given the risk of less strength.

James

Peterjfinch · 09-12-2010, 09:24 PM

Quote:

Originally Posted by larby

To be honest, I'd love to reply but don't want to risk being out of my depth and getting something wrong. Personally I'd make it as close to original spec as possible, any weight loss probably wouldn't be worth it given the risk of less strength.

James

Thanks James,

I appreciate your honest and genuine answers. It´s a shame we don´t have any professional people on her, people like boat builders or designers. Even a good marine engineer should be able to give some guidance, I would have thought.

Anyway, I guess it´s back to the drawing board with my pencil and rubber (no CAD programs or stress calculators etc).

Although the original crossmember was heavy, it was quite primitive (as photos) and my concern is, to reproduce this and move it forwards, then put more weight onto it.....Could this be a problem. My thoughts were to spread the weight over both steps and use heavy aluminium, with strategically placed weight bearers.

Oh well, back to the search engines and asking favours. Thanks again James.

Pete

larby · 10-12-2010, 07:13 AM

Oh there are plenty of them on here, Tony who has been helping you is one of them. Others tend to shy away from this kind of situation for their own reasons.

Ref. your crossmember, I would build in strength by design rather than sheer bulk to give the same strength with lighter weight. Corners can be braced (to create triangles) and the same idea can be applied to move forces exerted on weaker areas to places with more strength, or to change the direction of the force to a more manageble angle. Ie, the vertical weight of an engine on the centre of a beam could be transferred to a near horizontal force on the base of a longit with a simple brace.
Likewise, any flat sides can have material removed from drilling out circular holes in them. So long as you don't go close to the sides, keep the hole size sensible and leave space between each hole the strength of the structure won't be affected, but it will be much lighter.

As for ally versus steel, personally I was going to make my engine cradle from stainless. I'd say it's easier to snap 6mm ally in half by repeatedly bending it back and forth than it would be with 1mm stainless. Bear in mind you'll need more ally to give the same strength as steel, negating some of the weight loss. Others on here know way way more than me about the properties of various metals and their grades, so hopefully someone will chip in.

One last thing, make sure the longits/stringers aren't specifically stronger where your crossmember currently lies if you're moving it forward. For example, some, albeit newer, boat's stringers consist of a wooden engine bearer at the back, with the rest being foam. Moving an engine mount 18" up a stringer like this could give interesting results!!

Hope that helps and I'm not too wrong in what I've said,

James

Peterjfinch · 10-12-2010, 05:12 PM

Quote:

Originally Posted by larby

Oh there are plenty of them on here, Tony who has been helping you is one of them. Others tend to shy away from this kind of situation for their own reasons.

Ref. your crossmember, I would build in strength by design rather than sheer bulk to give the same strength with lighter weight. Corners can be braced (to create triangles) and the same idea can be applied to move forces exerted on weaker areas to places with more strength, or to change the direction of the force to a more manageble angle. Ie, the vertical weight of an engine on the centre of a beam could be transferred to a near horizontal force on the base of a longit with a simple brace.
Likewise, any flat sides can have material removed from drilling out circular holes in them. So long as you don't go close to the sides, keep the hole size sensible and leave space between each hole the strength of the structure won't be affected, but it will be much lighter.

As for ally versus steel, personally I was going to make my engine cradle from stainless. I'd say it's easier to snap 6mm ally in half by repeatedly bending it back and forth than it would be with 1mm stainless. Bear in mind you'll need more ally to give the same strength as steel, negating some of the weight loss. Others on here know way way more than me about the properties of various metals and their grades, so hopefully someone will chip in.

One last thing, make sure the longits/stringers aren't specifically stronger where your crossmember currently lies if you're moving it forward. For example, some, albeit newer, boat's stringers consist of a wooden engine bearer at the back, with the rest being foam. Moving an engine mount 18" up a stringer like this could give interesting results!!

Hope that helps and I'm not too wrong in what I've said,

James

Thanks James,

I´m sure there are too, just not sure why they choose to remain silent? Yes, Tony has helped a lot but I guess that sometimes he is a very busy man.

I will be looking much deeper, into the build-up, of the hull and stringers, tomorrow. At least I can then give correct answers to all the professional questions that will surely follow this.

What you say does make sense, I´ll have to play with some ideas I have and post them here, for your opinion.

Thanks again James.

Pete

Tony Davis · 10-12-2010, 06:22 PM

Quote:

Originally Posted by Peterjfinch

? Yes, Tony has helped a lot but I guess that sometimes he is a very busy man.

Actually, no, I'm not at the moment. Spending most of my days walking the dogs and sorting my workshop. However, I do only comment or advise when I feel I have something of interest or help to say.

Without actually seeing the job, measuring up, inspecting the longitudinals etc, it's very difficult to advise what is the best way forward.

As I said in an earlier post, I'd go for what was originally fitted, after all, Brian was no fool, so other than maybe galvanising and some powdercoating to the steel components, I'd be copying what was fitted from new.

Peterjfinch · 10-12-2010, 06:28 PM

Quote:

Originally Posted by Tony Davis

Actually, no, I'm not at the moment. Spending most of my days walking the dogs and sorting my workshop. However, I do only comment or advise when I feel I have something of interest or help to say.

Without actually seeing the job, measuring up, inspecting the longitudinals etc, it's very difficult to advise what is the best way forward.

As I said in an earlier post, I'd go for what was originally fitted, after all, Brian was no fool, so other than maybe galvanising and some powdercoating to the steel components, I'd be copying what was fitted from new.

I have an idea !?(%$&/(, bring the dog over here and I´ll look after it, swimming in the med, in the sun, long walks on the beaches, what more could a dog want?

While you´r here, dropping the dog off, take some measurements and that will give you something to do, when you´re not sorting the workshop?

An idea?

Pete