Redesigning a step boat

Im looking to build a step boat 14-15 foot.

I have the plans on hand, but im planning to put a bigger engine in it, than descriped.(not weigth, but hp).

So i wass thinking to make it a couple of feet longer, with steeper keel, and maby make the step higher. For stbility and speed.

make the popeller maby 1-2" aft the boat. insted 1 foot from aft, under the boat, and the rudder placed behind indsted of under the boat. this making the shaft decline smaller, and more power backwords insted of downwords.

dos this make any sense, or is i hippi di hop.

Regards BM

 

Step boats are not as easy as might appear. Step design and location along with weight distribution are critical. Suggest you look at some of the latest material published in Professional Boatbuilder or other sources.

That said, and ignorant of all the rules, a friend and I had a 14' step boat in the fifties that ran well and planed both of us to at least 15kts with a 6hp Wizard outboard.

 

Oh, its not that hard, especially on a little boat where you can move the CG around so easily.

Put the CG at the step. One step. Same angle of attack forward and aft of the step.

 

A good rule of thumb is to keep the step aft of midship. I wouldn't suggest going any deeper with the step. This would only tend to make it less stable on such a small boat. A depth of about 1\2" would be more than adequate. Going deeper with the keel will add more deadrise again making it less stable at higher speeds. Depending on what the final deadrise is and depending on if you have and where you locate your strakes\or A pad. I don't think I would go more than 12-14 deg on the bottom unless you plan on being in sloppy water often. Hope this helps.

Ken

 

You may be interested in this. It is a 30 foot boat, weight 2000kg, 550 Hp. Here are the stepped running surfaces.

 

VT,
Thanks that is interesting. It Really all depends on what purpose of the design. Reversing the camber on the bottom achieves lowering the keel for sure and breaks the surface well. That also keeps the average deadrise or height of the chines above the keel line reasonable. I still would avoid steps of that depth esspecially multiples For a smaller boat of this size. Even if kept to scale.. Not saying they can't work but certainly not for the novice. What are the Performance and handling characteristics of the example boat like? Interesting thanks for sharing. What Part of London are you from. My Dad Was from London prior to moving to the states to work with Post Yachts in the mid 60's.

Regards

 

actually i decidet to build a nother boat. it a singel hull with out step.

I will build a model af it in 1:5. and then test it... I woud like a redesign of it, for a more slik design, and stabilitet.

But all in models, just to get the right lines and no funny result with the real one.

//BM

 

QST: The handling is yet to be determined. A two meter model of this boat is being built for testing. The design concepts are *similar* but different to the Occe Mannerfeld B24 bat boat.

What I have done differently from Occe is to have a flatter V for the rear running surface, and ( you can not see from this ) a completely flat V pad at the transom. Additionally I have increased the aggression of the front step, which should help in the typical waters we have around the UK. This agressive front step is more like Lorne Campbell would design, and is similar to the setup of the BladeRunner.

The running surfaces are not wide for the length of boat, and this will increase chine walk, so I have a dual tail fin & wing upper deck to help control occelation, added to which the wings are cupped which exerts ground effect when underway.

I also have a shallow design for the upper deck which produces air effect lift.

 

several threads around on step design...look here and here.

 

Modle is ready

The model plug has been finished finally, and is ready to take the mould. I would guess 6 weeks before the first actual fiberglass boat goes into test.