"High Thrust" twins on a 25

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This is not a "single vs twins" question, I promise!

I was looking at outboard engine specs this afternoon, as one does when one is landlocked and temporary boatless, and came across "high thrust" engines from both yamaha and honda. Without being 100% clear on what this means, I noted the following weight differences:

2x90hp yamaha: 366 lbs x 2 = 732 lbs
2x60hp "high thrust" yamaha: 262 lbs x 2 = 524 lbs

2x90hp honda: 359 lbs x 2 = 718lbs
2x60hp "power thrust" honda: 256 lbs x 2 = 512 lbs

It appears to be a ~200 pound weight savings over a pair of 90hp engines, but I'm of course curious whether the 120hp would leave a C-Dory 25 underpowered.

The least HP I have so far seen on a 25 is 135hp, so my hunch is that a pair of 60hp engines wouldn't be enough. But I'm stuck on this idea of "high thrust," whatever that means. It appears to me to mean something like "optimized for lower speeds than other engines of equivalent HP," which is what got my mental gears turning a bit.

Do any of you folks have thoughts about this? Anyone run relatively smaller twins on a C Dory 25?
 
These High trust engines are mostly for pontoon boats and similar applications. I feel that 120 hp on a 25 would be too little. Some of the old 25 cruisers were powered with considerably lower HP--and were run as trawlers. Many of the 25's had the 130, and I believe several had a 115--the 130 was marginal in my opinion when fully lowed for cruising.
 
I think if you look at both engines a 50-60 hp ht and a 75-90-115hp regular engine the lower units are the same size
the 50-60 hp engines are running a 13-14 in diameter prop same as the 75-115 eng. The difference would be the 75-115 family could run a 13-14 dia. plus have a higher pitch then your 50-60 eng family

On the cd 25 the difference would be in top speed because the high thrust 50-60 eng would not be able to have as higher pitch as the 75-115 of engines .Having a cc-23 if buying new I would consider twin 50 high thrust engines
 
Totally agree with Dr. Bob. A lot of small sailboats use a "high thrust" outboard. I consider that to be more torque - good for pushing something to hull speed, but it's not going to give you the horsepower necessary for going faster. I think 120 hp would be too little for the CD-25. If all you were ever going to do was run at hull speed, one 60 hp motor would be way more than enough.

Best wishes,
Jim B.
 
I would consider two of the new Yamaha 70's. They are lighter and since a number of 25's use 135 hp singles they might make for a decent way to have the best of both worlds. Displacement speeds on one motor ought to to be able so save some money on fuel if you are not in a hurry.
D.D.
 
Thanks for the thoughtful replies, everyone!

Will-C, the Yamaha 70s sound like a really interesting possibility. According to the Yamaha website, they weigh in at 257 lb each (x 2 = 514lbs). I wonder if a pair of them would be sufficient for a 25? Their specs sure make them look promising.
 
Regarding the Yamaha 70: I haven't got time to look up the specs right now, but if I remember correctly, the maximum tilt angle for the 70 is a couple of degrees less than for the 50-60 motor. On my boat, at least, it might be the difference between the skeg clearing the water at full tilt and not. I think the weight difference between the 70 and the 50-60 is just a few pounds, but that would also tend to increase the chances of not being able to get the engines completely out of the water when anchored or moored.

The difference in tilt might be addressed by raising the engine slightly, but that might not be desirable.

This question of tilt range may not even be an issue for other boat models, or for boats used or loaded in particular ways, but my boat is in the water all the time and is often heavily loaded. Before I got the Yamaha 70's for my boat, I would have to be convinced I could get the engines all the way out of the water. (I'm not even seriously thinking about re-powering, but I kind of drool every time I see one of those 70's.)

Just one more thing to think about.
 
I always compare the "High Thrust" engines to the granny gear on a truck- used to get a heavy load moving at slow speeds.

In the case of the Yamaha F60 and T60 High Thrus, the difference in the lower unit gearing, allowing the High Thrust to turn a larger diamter prop. If put on a boat instead of an F60, you would runn a larger diamter, flatter pitch prop.

There's no magic- 60 horsepower is 60 horsepower. The difference is in the bite that the prop has in the water.

The larger gearcase has larger, more robust gears- again a good thing when pushing heavier loads. The downside is that there is more drag from the larger gearcase and big prop.

BTW- Mercury's Big Foot is the same idea- a larger gearcase to turn a bigger, flatter prop. On the Lunds we sell some models benefit from the Big Foot gearcase, but top speed remains the same.

Evinrude's 40-50-60 already have a geracase similar to the "High Thrust" models offered by others.
 
Maybe I am missing something--but the 70 is about 250 lbs equals 500 lbs for the pair--vs the 175 Suzuki at 485 lbs for a single....

You will have a better hole shot and top end with the single Suzuki, plus it will cost less...
 
That's a good point re: the weight of a single vs. the weight of twins. When I start thinking about a single, I mentally add in ~100 lbs for a kicker to go with it, although I don't know enough about engines yet to make a good judgement on whether I'd eventually decide one was necessary.

Cost is also sure to be a MAJOR consideration, one which I have conveniently not even begun to think about yet!
 
Since the poster had twins in the subject line hence my suggestion to consider the Yamaha 70. Some think that shutting down one engine and running at displacement speeds might be a benifet to fuel mileage. At the small weight savings the Suzuki with 35 more hp ought to have a better holeshot. As far as top end goes on a flat bottomed 25 is top end really at concern? I see a lot of 25's around with 135 hp Hondas. Maybe fuel at 5.00 a gallon is a concern.
D.D.
 
You guys have inspired me to dig a little more here. I put together a spreadsheet with a selection of motors along with their weights. I included both singles and twins, ranging in power from 130hp total to 200hp total.

For singles, I also noted that a kicker might be desired, and allowed ~100 pounds for one in a separate column. The list is sorted by the combined weight of the engines (single+kicker for singles, 2x engine weight for twins).

Here's the list:
list of some potential power options for a CD 25

Some things that are not on the list are surely very important, including:
* cost
* availability
* reliability
* noise

But I thought it was an interesting thought experiment anyhow. This discussion has been extremely informative for me![/url]
 
I seem to remember this topic coming up before. I was always in support of smaller twins on a 25 and as an owner of a F70 powered boat now, I can say it is a light and powerful but quiet motor and I would not hesitate personally to power a 25 with a pair of them given the chance. They do have a 25 inch length and I think the power would be sufficient for most owners and twin redundancy is there of course. I really doubt if one motor could plane the boat but the right prop might make it possible. We could just barely plane on one 90 heavily loaded with a relatively unsuitable prop for that purpose.

I have also been known to use a crescent wrench as a hammer if provided with "proper" justification.

We average over 7mpg at planing speeds pushing a 90+ inch wide medium V hulled aluminum loaded with a similarly heinous amount of gear as we carried in the 25 minus a dinghy on the roof of course.

Another fan of this motor:

http://www.c-brats.com/viewtopic.php?t=17279

The advantages over twin 90s would be lighter weight, lower cost, lower fuel use (likely) while retaining the whole twins are better concept.

That said, I also think a 175 or 200hp single is hard to argue against given long stretches of smooth water.

The honda 60 units may also stand a chance but I do not have experience with them.
 
svmegatron":1yvhmkig said:
You guys have inspired me to dig a little more here. I put together a spreadsheet with a selection of motors along with their weights. I included both singles and twins, ranging in power from 130hp total to 200hp total.

For singles, I also noted that a kicker might be desired, and allowed ~100 pounds for one in a separate column. The list is sorted by the combined weight of the engines (single+kicker for singles, 2x engine weight for twins).

Here's the list:
list of some potential power options for a CD 25

Some things that are not on the list are surely very important, including:
* cost
* availability
* reliability
* noise

But I thought it was an interesting thought experiment anyhow. This discussion has been extremely informative for me![/url]
Click to expand...

Love the chart-
Couple of notes-

Evinrude 130 should be either the E130DPL (blue 20") or E130DSL (white 20"). This model is even lighter than the 25" model. The DPL / DSL designation holds true for all E-Tec models in this application. If you want white choose DSL.

For Yamaha models, they should be F70LA, F150LA, F75TLR, F90TLR

Suzuki Models end in TL to indicate 20" model.

For the record- Evinrude models are weighed with cowl, oil and prop. Competing models are not always weighed the same way.
 
You have mixed 20"and 25" motors on your spreadsheet .
All the published weights are for the shortest shaft length and dont include props or fluids [which on twins can be another 30 Lbs.]
The C Dory 25' can ONLY run 25" motors .
So.... 70 Yamahas and most all 60s and under are out, as they dont come in 25" or counter rotation [not necessary ,but nice].
All motors with an L in the model # are likey 20"
If the have an X they are 25"
Marc
 
I don't know where they list it, but it is not available to US dealers.

Mercury's 60 Horse Big Foot is listed as being available in 25" version.

I forgot the 25" transom height of the 25'.
 
A few comments: The Suzuki 140 is a fairly "weak" motor--and I compare it to the Honda 130--probably not the best outboard for a 25. (I own one on a Caracal--and performance is closer to the Yamaha 115 I owned than the 150's I have owned).

You add 100 lbs for a kicker. We just have used a dinghy motor (3.3 hp at about 30 lbs if absolutely necessary to get "home"--but again back to the argument that modern outboards are very dependable....as are modern car engines--most likely problems are gong to be bad fuel, or run down batteries. Both of these are preventable, and would potentially disable twins. If you want a trolling motor--there are some cases where a 6 hp or 8 hp would be nice. But getting back to my experience with a sailboat hull very similar to the C Dory 25 (weight more, air resistance about the same, more wetted surface area with a fin keel--and running only a 5 hp outboard for many hundreds of hours which gave 5 miles per hour.

If for some reason you have to have twins--it looks like the Yamaha is just not available in the US--so the question is moot.
 
Er, yes, transom height! Confession time: I kind of thought all motorboat transoms were the same. I'll add that to the ever-growing list of things I had no idea about :-)

As a landlocked and currently boatless person, this is all incredibly interesting to me. When I finally manage to get back into boat ownership, I am almost certainly going to be using that old standby, "The Previous Owner's Motor."

Mr Thataway's point on kicker weight is well taken - I picked 100 lbs as a nice round number but if a smaller, lighter engine would work for the purpose that would be just as good.

On the subject of a kicker, if the most likely things to disable a motor are fuel and battery, maybe one of those new propane powered outboards would be a good get-home emergency engine. The 5hp weighs only 52 pounds. It might push the boat at 4-5 knots in calm water (<- this is a totally uninformed guess on my part), but it would be totally separate from the main engine by virtue of its being a pull start *and* a totally different fuel. Of course, one would have to carry propane for it ... hmmmm. It bears thinking about.
 
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