Weight vs Size

[williams359]

Will a engine push a 3.8m (air deck) sib at the same speed as a 3m sib (aluminium floor) if they weigh the same. Will one plain easier than the other.

[Landlockedpirate]

The simplistic answer is no, the heavier, longer sib in general, will be slower.

However boating is not that simple, lots of other factors will effect the speed, including wave height, amplitude, wind speed, loading etc etc. In some circumstances the longer sib could be quicker because the shorter sib wouldnt be able to plane due to loading or wavelength.

[williams359]

They weigh the same

[Landlockedpirate]

Still the same answer, assuming they have the same hull design. The longer sib will have more drag, hence slower in most conditions.

[Starovich]

however, the stiffness in the hull will result in more engine power being translated into forward speed.

[williams359]

It maybe better to ask has anyone gone from a Honwave T30 aluminium floor 54 KG to the T38 air floor 49 KG and kept the same engine.

[kaman]

On the weight vs size issue I can only add this.
I changed from a 3.3 m aluminum floored Plastimo to a 3.5 m aluminum floored Honwave.
The Plastimo was 20 kg lighter than the Honwave.
The Plastimo had a smaller floor and smaller tubes and consequently was less buoyant.
I powered both of them at one point with my 2.5hp Suzuki outboard.
With two persons aboard and fishing gear the Honwave was noticeably faster.
I think this can be attributed to it being bigger / more buoyant and displacing less water than the smaller narrower Plastimo.
Just something to consider.

[Big Al C]

I went from a 270 sunsport air v floor to a bombard aerotec 380 using mercury 15hp. 22 mph for the 270,,,,, 20/21 mph for the 380,,, 380 about is about 7 kg more and just over a metre longer. With no real drop in speed, I put this down to the shape of the hull.

[Locozodiac]

Will depend on the engine used, a smaller engine than max transom rated will slide, achieve better fast displacement speed, plane faster a 380 sib than a 300 one, more hull drag issues to overcome faster compared to less hull drag on the 380. Get yourself a 2 strokes Tohatsu 18 HP, will plane anything more efficiently than any other 15 HP engine. Take my word for granted...

Happy Boating

[Landlockedpirate]

Originally Posted by Big Al C

I went from a 270 sunsport air v floor to a bombard aerotec 380 using mercury 15hp. 22 mph for the 270,,,,, 20/21 mph for the 380,,, 380 about is about 7 kg more and just over a metre longer. With no real drop in speed, I put this down to the shape of the hull.

I'd put it down to the hugely overpowered 270

[Exe treme]

Originally Posted by Landlockedpirate

I'd put it down to the hugely overpowered 270

Heheheh, you mean like this?

[Landlockedpirate]

Originally Posted by Exe treme

Heheheh, you mean like this?


Attachment 92651

That looks fun

[rossymtb]

Had a 2.7 airmat floor with 10hp merc
Then upgraded the boat to a 3.8 aluminium floor. Defiantly quicker, takes less to get it to plain. And can carry more weight

Nicer as well when fishing to stand on a solid floor. I'd go for aluminium floor

Then upgrade the engine to a 25hp. Notice the difference again