Power Thruster

tommays · Feb 1, 2012

Just by the right high thrust prop and the boat will move fine as they have spent a kabillion dollars on outboard lower unit design over the last 80+ years and no outboard factory has seen fit to use it

4HP vs 8000# 29' 4 HP wins and brings boat home 16 miles at 4.5 knots

MrBill_FLL · Feb 1, 2012

there are several owners on the macgregor board that made their own. but its a complete ring.

they say they work, and are safer.
*no 1st hand experience....

tommays · Feb 1, 2012

What did you buy ? as the standard blades are for planing hulls

A high thrust has more blade area with a very small pitch which allow the motor to reach its rated RPM and it is the only way it can output its rated HP to move the boat at slow speeds

Benny17441 · Feb 1, 2012

It's been around for a while, if it was that good I would have heard of it sooner.

tommays · Feb 1, 2012

In your blog you say you have a June 2009 8hp Tohatsu outboard for which they make 5"/ 6.5" / 7" pitch props and make no mistake if you want the boat to move in adverse conditions its GOTTA scream to make the 8 HP

If your not sure then a item like a tiny tack would give you some assurance of the motors RPM

Also keep in mind a 4HP moved the Cal 29 at 4.5 knots and while the now like brand new A4 inboard will push the boat above 6.5 knots its really not efficient to go much over 5.5 as you use about twice the fuel for that last knot

MrBill_FLL · Feb 1, 2012

search for 'walt' (from CO.) on the mac board. he has that engine, and tested some props...

he also has the ss prop ring.

this is for the H27? whats the displacement? less than a mac26 I'll bet.

Rick D · Feb 1, 2012

Shroud

A guy I used to do some work with designed the unit. The inspiration, if I recall correctly, was tug boats.

Mike B1026 · Feb 1, 2012

I have one. Main reason was to protect the rudder from the outboard prop. I would imagine changing the prop would be more help for power though.

I believe some tugs use a similar design for more thrust.

AtlanticAl · Feb 1, 2012

FourPoints said:
I've seen the power thruster for sale before, but I notice it's now sold here at the SBO store (http://shop.sailboatowners.com/prod.php?50097/Power+Thruster+for+Sailboat+Outboards). Originally I thought it was a gimmick, but after some thought I realized the idea has some merrit, but I assumed the claims were way over exagerated. Now seeing it sold here makes me wonder if it really does work as well as they claim.

Has anyone here used it before, and can you attest to how well it actually works?

I have a Tohatsu 8hp, and I really wish I had an extra 2hp for rough water.

I see this and have wondered for a while if it would help give that extra thrust needed without replacing the engine, as well as possibly reduce cavitation when the prop gets near the surface in bigger waves.

Thoughts?

I can almost guarantee, that wont work. Many years ago, i worked for the Scottish Fishery Protection Agency, we used Pacific 22 RIBs, launched from a mother ship, we would then board fishing boats and check their catch and nets. They became so concerned with the idea of a man falling in and being run over by the boat, that even though it had never happend, they ordered us to fit guards to all the fast boats, just incase someone got injured by a spinning prop. The guards were duly fitted, they look just like the thing you posted, apart from, they went all the way round the prop, i was the first to test out a boat after they were fitted, it had cut the performance of the boat in half. Prior to the guards, the boat could run at 32 knots, after the guards, it couldnt even reach 20, and it felt heavy, and was slow to get on the plane. The boats used a lot more fuel, but, we were told they had to remain on for safety sake.

kloudie1 · Feb 2, 2012

Here is what the device is based on:
http://en.wikipedia.org/wiki/Kort_nozzle
Note that the effect is negative above 10 knots.. The thruster is a partial Kort .. which helps with the mini cavitation and tip vortices on the upper part of the prop, close to the surface.. It probably does increase the low speed thrust by a noticeable amount..

Bill Roosa · Feb 2, 2012

I'm having trouble understanding why some folks are using a motor in what are clearly windy conditions. iF the wind is blowing, as indicated by there being waves, then putting up those big white cloth things attached to that big metal pole in the center and the wires that hold it up would seem to be the answer to moving forward. it will most certianly stablize the boat and give you a better ride.

walt · Feb 2, 2012

Not sure there would be anything interesting looking at my old posts.. I do have a prop guard ring - but it’s because on the Mac 26S, if the rudder swings up to about 45 degrees, it can meet the prop (this happened to me one time in a rudder grounding).

Just as a data point, I’ve had both a 8 hp Honda and a 9.8 hp Nissan (both four strokes) on the Mac 26S and with props on both ranges of the spectrum, I can easily cruise at 5.2 to 5.6 knots at about half throttle. A lower pitch prop just operates a higher rpm than the higher pitch prop - either easily gets the boat up to hull speed. My boat is substantially lighter but note also the 4.5 knots from a 4 hp on the Cal 29.

I wonder if the outboard isn’t putting out full hp? (and keep in mind that my data point is in calmer conditions)

FYI, prop guard ring or not (probably different than the thruster), I cant tell any difference in performance..

Benny17441 · Feb 2, 2012

The h27 is a lot of boat for an 8 HP outboard. The best prop for it would be the largest diameter you can fit with a moderate pitch that will allow the engine to reach its rated RPM. No auxiliary engine includying small diesels can buck a strong wind head on. When the wind is up the power is in the sails so turn the kicker off and pick a point of sail where the VMG to destination is higher than what you were getting with the engine.