Tube ends: cone style vs rounded. Which is best?

[mooseknuckles]

Thinking of getting a 14ft inflatable and will be matching it to a 20hp Tohatsu 4stroke. Can someone explain the benefit (if any) of going with a boat that has the rounded ends vs tube ends that are cone shaped.

Do the rounded ends perform better than the tapered cone style or vice versa?
Thx very much

 

[Sea Rider]

Re: Tube ends: cone style vs rounded. Which is best?

It's an eye catching issue, there are 4 end cone shape models to choose from, will depend on the manufacturer which to use, On some sib/rib models you can have extended tubes with complete vertical cones, lid type.. Personally preffer the traditional end cones because having a solid end cone protection compared to a vertical flat end cone.

Some manufactures like Mercury state that their new end cone design which is bit larger/flat will plane sib faster, probably if sitting way back at transom area as will act as trim tabs, no difference compared to other end cones if ballancing sib correctly from the start.

Happy Boating

 

[CO2cylinder]

Re: Tube ends: cone style vs rounded. Which is best?

I think one of the major reasons for the rounded cone ends is to provide additional buoyancy at the stern of the boat to accommodate the higher weight of 4 stroke outboards, since the lighter 2 strokes are unavailable.

 

[ssobol]

Re: Tube ends: cone style vs rounded. Which is best?

In theory cone end tubes will give better performance because there will be less drag as the water will flow past the end of the tube more smoothly. A rounded or blunt end tube will generate an eddy in the (relatively) low pressure area behind the face of the tube which sucks water towards the tube. If you look you can see this when the tube is displacing water (slower speeds). At high speed with the tube planing the water will flow straight back in either case if the tube is riding on the water surface.

That all being said it probably does not make a practical difference in real life. Perhaps you might see a difference in fuel economy if you operate the boat a lot in displacement mode.

Zodiac has been making cone end tubes for a long time. Longer than 4 stroke O/B engines have been commonly available. Newer boats have blunt end tubes (e.g. Nautica) or rounded end tubes (e.g. Walker Bay) and these are delivered with 4-stroke engines. I don't think that the shape of the tube end has anything to do with the engine fit. It is most likely either styling or cost of manufacture (i.e. it was probably easier at one time for Zodiac to thermoweld a cone shape than a blunt end on a tube). However, most of the more recently developed Zodiac boats have rounded tube ends, only the Classic and Pro series still have cones.