increasing bouyancy in a deep v hull

[myusernam]

if you put an ali full length pod on (basically lengthen the boat in ally) on a deep v do you really increase the weight the stern can carry? I.e. if a skinny deep v is only comfortable floating 100kg's at the stern, and then you extend the stern with the same v for 400 mm, dont you have the same problem? is the only real way to add boyancy either side of the motor (below waterline at rest?) like a step.

[Moffy]

Will depend on the rest of your weight distribution - adding the pod will increase the volume of the boat and overall lift - if no other weight is moved aft - then yes you will increase what you can "carry" at the new stern based on overall weight distribution over the length of the hull (i.e same weight motor should sit higher with the full width pod as all other weight is further forward (relatively). Now this is probably a pile of sh1t - hopefully others can confirm...... (there's a few beers behind the logic............)

[gofishin]

It all depends on the shape and volume of the pods and the hull, and the mass of both and CoG of hull, and what you are moving around...in simplified terms.

There are two design considerations; CoG (centre of gravity) and CoB ( " " buoyancy).

By adding a full pod and moving your motor further aft, you are changing (moving aft) both the longitudinal CoG and CoB. In simple terms, if the CoB moves (relatively) further aft than the CoG, you are creating static lift at the transom.

It would also depend on sizes and style of the 'pods either side' vs the full pod. A lot more water is displaced in the centre of a deep vee than out towards its chines, hence more buoyancy/lift.

Sorry, no one can really answer your question without a proper analysis.

However, adding pods either side on the transom of an existing boat will definitely create static transom lift . The more water displaced the more lift is created. What this does dynamically is another question!!
Cheers
Brendon


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[chris69]

Dont reinvent the wheel buy another boat thats more suited,when you add to a boat your changing everything as mentioned above and what info that is on the build plate!!!!!!

[GBC]

Pods either side will float a motor at rest no problems. If they are wetted underway they will have a couple of effects.
1. They will require the engine be set deeper than normal due to the extra stern lift
2. They will all but negate the trimming ability of the outboard due to their larger running surfaces at or about the rear of the engine.

Take one of the original 4.5 polycraft for a strap for a demo of the above. This isn't a terrible thing when done correctly as polycraft did, but it is a thing. Such is the inability to bog the rear of a poly, you can perform cutback manoeuvres on the faces of waves in bars and other fun manoeuvres such as power slides on boat wakes (stern lift makes the prop vent). All good fun but it doesn't actually do anything much helpful. Trimming the motor in and out yields some change in the boat's attitude, but much less than with traditional sterns because the hull wants to run naturally. Get the pods wrong and you're going to have a dog of a boat.

extending your whole boat by 400mm just makes it a bigger boat. Bigger boats carry bigger motors for all the reasons the other guys said. Again, may or may not turn your boat into a dog.

[Chimo]

mYn

Obviously a different boat ( a ten ft tinny) but the addition of a pod on either side of the motor did prove positive in that it increased rear buoyancy and lengthened the boat running / planing surface with the result that the boat runs flatter and planes easier and earlier.

At speed the pods act more like a set of Lencos that are trimmed fully up.

Its when the boat is stopped or slowing that the lift at the stern is obvious. Each pod appears able to support around 100kg as one can now stand on them and be supported.

Perhaps before committing to building a complete pod across the rear of the boat and possibly getting unwanted outcomes you consider a smaller pod on either side with the motor retained where it is now. If you want to fit a heavier motor in the future you could test its likely affect by adding equivalent weights to the top of the pods.

Can you fit pods under the existing rear steps and use these as part of the connection to the hull.?

Pics of my pods are on the site.

Cheers
Chimo