Twin Suzuki 60s on CD22

jingram · Posted: Fri Jul 20, 2012 1:05 pm Post subject:

Well clearly, I totally blew things out of proportion or misinterpreted tone and for that I apologize.

Bob, once again, just so we are clear, my apologies to you.

Chimoii... so help me out here. I've read that prop diameter has little to do with thrust or torque. Pitch does. According to what I have read, the prop doesn't deliver torque. It provides thrust based on torque applied to it by the engine. Is that the case or am I missing something?

You are absolutely right, I was using torque incorrectly since ultimately it is the thrust being provided by the props that are spinning up hard do to a torque dump by the motor that would ultimately put the most strain on the transom. I definitely think it could be harder on the transom with one bigger block motor than two smaller twins. The load, as you indicated would be slightly more spread out on with the twins instead of localized to one spot in the center of the transom which is the weakest point in the span.

This stuff really is interesting!

Will C -

Matt Gurnsey · Posted: Sat Jul 21, 2012 2:37 pm Post subject:

Since we're just spit balling ideas here-

Has anybody got twin Yamaha High Thrust 50's for power? I'm wondering what the larger diameter props would do for performance? Or would any benefits be negated by the increased drag of larger lower units?

The Evinude has the larger gearcase standard and the twin 50 and 60 E-Tec powered boats seem to be good performers.

Just thinking out loud....

Spike · Posted: Sat Jul 21, 2012 4:23 pm Post subject:

Hey Matt these are the ideas we are supposed to be kicking off of you!!

Matt Gurnsey · Posted: Mon Jul 23, 2012 2:23 pm Post subject:

I can give theoretical thoughts on the issue, but wondered if there was any real world experience. Cool

Yellowstone · Posted: Mon Jul 23, 2012 3:39 pm Post subject:

Jingram - I have been running the CD 22 for about sixteen years. The first had a 90 Honda and the second a 115 Merc. Thataway's comments are sound. The only reason I went to the 115 was because I now boat at altitude, near 8,000 feet which translates into a 24% drop in power compared to boating at sea level. On Yellowstone Lake at WOT with several passengers and gear, the top speed is 27 mph with the 115, but in the mid 30s mph at 3,000 feet, much too fast IMO for secure handling even with tabs. I use a 13" wheel. If I were boating at sea level, a 90 hp of any make would be just fine. Plenty of power. I find the tab setting at 60% and 4,000 to 4,200 rpm to give a firm, yet reasonably efficient way to go at speed. When time is of no concern, I cruise flat at 1,000 rpm and get close to 10 miles per gallon of fuel. Of course all of these figures have to be adjusted for weight aboard, wind, current, etc.

Have some info from a mechanic up here in Yellowstone about the Honda 40 with carbs. The outfit which rents boats at the marina has equipped a fleet of 16' Gregors (w/ swept up bow) for tourist use - 16 skiffs. These are used hard for 3 mos of the year, and usually run wide open in very cold water by people who know little about marine motors. Each motor is run for about 5 minutes before the tourists start using them. With routine maintenance, these motors are almost without exception trouble free. bullet proof in the words of the mechanic who is very experienced with marine motors of many makes. When the tourists runs into the bottom along the shore which has fine granite gravel and specs of obsidian which gets sucked up into the water pump and cut up the impeller, nothing else seems to go wrong according to him. He feels all outboards while in service should be started up daily and run for a few minutes even if not used for propulsion. Food for thought.

Yellowstone John

Miafun1 · Posted: Mon Jul 23, 2012 9:22 pm Post subject: Overpowering

I'm with Thataway. Even if you over power just a bit, you are opening up yourself to problems if there is ever a cause to be looked at closely by law enforcement. Its an unnecessary liability risk.

jingram · Posted: Mon Jul 23, 2012 11:24 pm Post subject:

A lot of you mention top speed and I don't think anybody here disagrees about there been a very finite limit to the safe handling capabilities of the C-dory hull. Everybody pretty much agrees that above 28-30 and things get squirrelly in a hurry.

Out of curiosity, are you all happy with the overall "pep" of your setups loaded for cruising? I'm not talking about neck jerking speed out of the hole shot, but rather, ability to quickly get up to speed as you ramp up throttle when you are running a typical cruising load... full fuel, water, and at least two people, plus whatever you are packing for food, beverages, etc.

Are most of you happy with throttle response and ability of the motors and the boat to respond to throttle commands quickly in these situations or those of you running say twin 40s or a single 90, does the speed come on more gradually and throttle response is more sluggish?

rogerbum · Posted: Tue Jul 24, 2012 12:12 am Post subject:

Hunkydory · Posted: Tue Jul 24, 2012 12:20 am Post subject:

I run the twin Honda 40's & don't want or need to run anywhere near a top speed of 30 mph. We run either very heavy on our Southeast Alaska cruises or medium at Yellowstone's high altitude, so are now propped for either with a 10x12 stainless prop that from memory gives a max speed of 21 mph at 5800 rpm. The hole shot is satisfactory with a ease of reaching planing speed. I have yet to find a bad water situation where more power would have been useful, but have no doubt that it could happen. In my situation having both Permatrims & trim tabs is a necessity for the way the extra fuel & other stuff for long range cruising is distributed. On our resent three month Alaska cruise of 2100 miles approximately 86% was done at displacement speed & only 14% at roughly 4500 rpm & 14 mph. 14 mph is my preferred cruise speed when on plane, so this worked well for us, but there is another situation where I believe more torque & perhaps hp would be very beneficial & that's when running on one motor at displacement speed. There it takes almost 3000 rpm to do 6 mph & 3500 to do just over 7 mph, so can not come close to Yellowstone John's 10 mpg & at 3500 rpm am concerned about possibly lugging the one motor, so only rarely do so.

Jay

Will-C · Posted: Tue Jul 24, 2012 10:19 am Post subject: Twin Suzuki 60s on CD22

I think the main reason the factory upped the horsepower rating from 100 to 115 was that almost no one had 100hp motors for sale anymore and for whatever reason 115hp became the new spec. There was a case with a Tomcat where a dealer put on two 175 hp Suzuki's on the boat that was rated for two 150's. They called the factory and the weight was the same so the factory gave their approval for the higher horsepower. Rigging a boat so it's easier to get into the squirrelly zone of beyond thirty mph in the case of a 22' cruiser and spending extra 1000 dollars money to do it seems like something only a government agency would do. I would be happy with twin forties or twin 50's. If I had it to do over I would have rigged our boat with twin 70's if the new Yamaha 70's would have been available at the time.
D.D.

Yellowstone · Posted: Tue Jul 24, 2012 12:47 pm Post subject:

I can't cite the tests done, but I have read where a single engine will out perform twin engines of the same horsepower combined. Seems that extra mass in the water from twins creates more drag. Also, twins may weigh more than single engines of same hp. But as the old saying goes, when you have the ponies, you have to feed them. There is no free lunch when it comes to efficiency. Interestingly enough, when on plane with tabs set at 60% (down), my 22' gets its greatest speed as measured by speed over ground with the GPS. Also, in a very light chop, speed is higher. Someone told me that the "tension" is broken on the hull little bits at a time, with less wetted hull in the water??? The CD 22' is much more weight sensitive then is generally understood. I'm not sure what the "critical mass" is, but when heavily loaded, I travel a little bit over hull speed. But then everyday is late Friday afternoon to me. Yellowstone John