pod technicalities

[BM]

Noel, He was talking about going to a 25 inch engine, and if that hull is set up for a 20 inch engine he will need to jack the engine up higher. No confusion there at all. Nothing to do with pods. Only transom heights. Take any boat with a 20 inch transom, you cannot mount a 25 inch engine directly to the transom, the trunk is too long.

SO70, its not about calculations mate. The purpose of the plate is to allow the pod to be fitted as close to possible to the bottom of the hull to minimise any canti lever effect caused by a stepped pod sitting 8 inches from the bottom of the hull.

But to each his own. I'll stick to fititng pods to my customers boats in a manner that I know works.

[Noelm]

hhhmmm I must have misread/interprted what was being stated, I thought he was making some new pods, and as such he can make them to suit any shaft length, and I agree about the 'top lip" height (that is what I said, I thought) what I was trying to relay is that regardless of shaft length, the cav plate remains in the same running position, a lot of people think that if you go to a 25" shaft, you have the propellor 5" lower in the water (if you get what I mean) and that is not the case, it is very hard to put into text your "minds eye" and can be confusing.

[BM]

Agreed. I just re-read it all. His concern was the right height to set the mounting area.

I would not have thought many people would think the gearcase is 5 inches lower in the water with a 25inch shaft? Or perhaps they do?? I guess we take it for granted sometimes that others understand what we understand?

Cheers

[MICK H]

Thanks fellas i understand what you are both saying {same thing different piece of string} . I'm making a mould off the back section of the hull so the pod bottom is an exact extension of the hull.I will use this section to make a dummy pod first so everything is spot on and then i'll take a mould from that, and that should just about do it.This might sound like a lot of bother but i use fibreglass and a lot of apoxy and stuff like that for work. A lot of materials i already have so i may as well use them . Is formwork ply ok to use to fill in the transom ?
Thanks again......Mick

[FNQCairns]

NO the phenol covering doesn't let the fibreglass get a grip and it will soon enough de-laminate, CD grade ply is OK or sand the phenol black off your form ply.
Be sure when you drill the engine mount bolt holes you drill oversize fill with epoxy then redrill correctly for you mount bolts. Some glue with epoxy a piece of bolt sized conduit or SS tube to help with crush if a less solid structure is used like foam or core material.

cheers fnq

[BM]

Be sure when you drill the engine mount bolt holes you drill oversize fill with epoxy then redrill correctly for you mount bolts. Some glue with epoxy a piece of bolt sized conduit or SS tube to help with crush if a less solid structure is used like foam or core material.

cheers fnq

I am intrigued by this most unusual approach!! Please explain your logic.

Cheers

[FNQCairns]

Hi BM depending on what structural component is used within the pod (can be solid FG) if some of the more exotic materials are used (relative to wood) they can have a tendency to crush so a crush tube set sensibly shorter then the total thickness can be used, mostly epoxy is the glue of choice.

If wood is used depending on what the builder decides he may also use a crush tube but filling and drilling does away very nicely with the opportunity for water logging.

As you would know, every step is dependent on what construction is going to be used.

Mick if it were me I would use CD grade ply, iso or vinyl ester as the resin, and use chop strand only as the separating layer between multi axial glass, can be very strong for thickness/weight/time/cost than an equivalent predominantly chop strand layup and let it cure for 2 weeks.

Cheers fnq

[BM]

Fair enough!! You have your reasons and have explained them well.

However, if you placed an alloy bar (say 50mm high, by the width of the clamp bracket area and say 10m thick) drilled to the bolt hole pattern, so 2 bars, 1 for the top bolts and the other for the bottom bolts, then compression of the timber would be minimal given the surface area provided by the bars.

Although, even that extent is (in my opinion) excessive and some large flat round washers inside the pod are suitable for the task.

Look at most new boats, bolt heads and washers on the inside of the transom. Sure they will pull in over time. So perhaps we should fit a plate that mimicks the clamp bracket and then attach the nuts to the bolts? This will certainly spread the load a lot better but is it warranted?

Definitely not knocking your approach. Questioning it YES, knocking it NO. We all do our things a little differently...

[SO70]

Mick,

One inch up for every 12 inches aft. This is the general rule of thumb.

1) Pod length is usally worked out on the basis of the engine being able to trim up fully. Typically 600mm will achieve this (probably even 550mm will do). This will of course be altered if you incorporate a mini splashwell in the transom.

2) Your engine mounting height will be determined by the height you set the pod at. EG: when I fit non full depth pods I set them as low as I can get them. This then requires an alloy plate (I use 25mm thick) which is sandwiched between the engine and the aft end of the pod.

3) Either marine, or structural ply (both have the waterproof glue and will be suitable) on the engine mounting face. I would not use core mat as I don't believe it has the strength.

Cheers

BM, calculations do come into play when playing with non full depth pods.
if you do the calculation right there is no need for the aluminium plate between the back of the pod and the outboard mounting face.

[BM]

To each his own SO70.....

Sure, if your only consideration is the height of the pod then yes you are correct. No plate is required.

However, if boat performance when fitted with a non full depth pod is more important (it is to me and to most people) then pod position is paramount and engine location is alterable.

But hey, whatever works for you is fine......... Not saying you have to accept my explanation. In fact I don't care!!! I know what works for my customers boats!! Thats all that counts.

Cheers

[MICK H]

This is the reason i started this thread, everyone has an opinion on what is best as far as pod construction, type and placement.I think it helps to hear everyones opionions, i can then make a more informed choice. Thanks all for your input.
If anyone else has anything they think might help then feel free............Mick