Engine position for Tiki 26

[patrick lennon]

I would like to ask what are the advantages and disadvantages of and outboard mounted off the the aft beam vs one located at the back of the cockpit . My plans specify these 2 options and I can't decide. We are into month 4 and hope to have her finished by end of Nov in time for the North East Monsoon . Cheers Pat

[Kenneth Gorman]

The more central the engine the less chance of cavitation if the boat is hobby horsing in a chop.

[Andrés]

I have the outboard off the the aft beam and off-centre. I works ok and it give's me a clear cockpit. As Kenneth said the better from the cavitation point of view is when the outboard is in the center of gyration, but it puts the motor in the cockpit, near the mast. I like my clear cockpit and prefer not to have anything fixed in it. Sometimes I have cavitation problems, but usually it disappears when I change direction a little or decrease the velocity. I still prefer the clear cockpit than putting the ouboard on it, but I suppose it is a personal matter.

[patrick lennon]

Thank you for the reply and info. I would think that the further aft the engine is the better the maneuverability?

Andrea's I am wondering what are the advantages if you mount the engine off center.

Pat

[Andrés]

I think that at a low velocity the further aft the engine could be better, because you have a greater lever arm. But I have no other boat to compare and when I bought her the engine was in this position.

The motor is a little of center and in this position it clears the main sheet (I suppose is for this reason that the motor is of center). When there are waves it is important to  raise the motor as high as possible, so it don't slam.  Also you have the tiller of the motor near one side of the cockpit, so it is closer to one of the seats. On the other hand, you have a good side and a bad side of the cockpit to work on the motor. In practise it doesn't have been a problem to me because the cockpit is free of obstructions so I can change very quickly my position.

[kim whitmyre]

The manueverability of the aft engine mount is unmatched... Gave up trying to post, what changed?

[patrick lennon]

Thanks for the pics Andres. Your motor when not in use is very far from the water surface, which is good. I have seen motors dragging there props at high speeds. Off centre seems like a good idea if one wants the motor well clear of the water ...Thanks for the pics they area great help.

Kim so it seams to be a trade off between maneuverability ( mounted Aft) and lessening cavitation (in cockpit). Also access is better in cockpit but one loses valuable space. Hmmm... something to sleep on. I guess the cavitation problem depends on sea state in the area were on sails.

Thanks again for your help  Pat

  

[kim whitmyre]

Patrick, I went from a long-shaft 20" motor to the extra long-shaft 25" motor and cavitation is nil...Of course, the prop is at the same level as the deepest point of the keel, which is where you want it to be! Pushes the boat better that way.

[kim whitmyre]

[patrick lennon]

Hi Kim thanks for the pics and info . Presently I have a 9.8 tohatsu with a 20" shaft I may have to buy A new motor . May I ask what is the make and hp of your outboard? Cheers Pat

[kim whitmyre]

Patrick, it's the Nissan (rebadged Tohatsu) 4-cycle 6hp SailPro model. The SailPro comes with the lower pitch, wide-blade prop designed for displacement boats. It weighs in at 55 lbs/25kg. The 9.8, depending on its age, could weigh considerably more. You don't want too much weight hanging on the aft end of the tiki. In flat water, the 6hp gets my lightly loaded t26 to 7 knts + at less than full throttle. In chop it's slower, but with judicious steering, ie, not trying to power straight at the swells, it still pushes the boat well.

[Kenneth Gorman]

Patrick,
Another option is when it is mounted in front of the beam is put a box over the engine and make a feature of it as Boatsmith has done on his smaller Tikis.

[boatsmith]

Let us use correct terminology here. Cavitation is when the prop or impeller tears the water apart. When the prop pulls up out if the water due to pitching the correct term is ventilation. This is less of a problem on newer outboards as they have rev limiters. On an older motor when the prop caught air it would not catch water the motor would race and when re-immersed would not grab the water again until the throttle was backed off. A real pain in the transom. With the new motors the motor cuts out before over-revving and when re-immersed grabs immediately. Much more cool.