20' center console and 90hp evinrude. What will cruising speed be?

[bluefishing]

I am looking at a 20' seacraft center console that is powered with a 1980's evinrude 90hp. Can this motor plane this boat? I don't load up the boat with extraneous stuff when I fish. Can anybody hazard a guess as to what my cruising speed will be if I buy this boat?

Thanks

[McGillicuddy]

Yes, it can. Probably cruise at 22-24, and top out around 32. Many were originally rigged w 85hp motors. Properly propped it will stay on plane down to 15 mpg or so w/o trim tabs.

One of the guys here was running a Seafari with 70. Another, "bitsamonkey," just posted some awesome numbers with a Suzuki 90. I think he was getting 6.7 mpg at 27 mph, and topping out mid 30s or so.

Fr Franks old Seafari was running an Optimax 90 with great economy and around topped mid 30s also. Its 100 lbs more than the model you speak of.

[bluefishing]

Thats good to know, thanks

[mrobertson]

If the boat is light then you will be surprised at the performance.

I run a 2005 yamaha 115 carb'd engine and i cruise 25 - 27 mph at 4200 RPM. WOT with a light load i can touch 35 mph on flat water.

The engine will be mounted higher than you think it should be. Mine is mounted a little over 1" ABOVE the keel and i wish i could go higher but i'd have to re-drill and dont want to do that.

Fishing 3 guys on the boat with gear takes maybe 2 mph off those numbers and doesn't affect my boat planing at all. I've yet to REALLY load it down, just haven't had the need but i think the performance would still be adequate.

[fly4navy]

I went through this same analysis when I bought my 74 20 ft. CC SF last fall. I had an outstanding 5 year old 90 hp E-TEC from my prior boat that I considered swapping over to the Seacraft. I don't think there is an absolute answer as to how happy you will be. In my case, I bit the bullet and went with a new 115 hp E-TEC. I carry a fairly hefty T-top but otherwise am fairly light. Right now I am able to achieve 27 kts. at WOT and I am comfortable being able to perform just as well with 5 adults on board.
I think your boat will perform allright with you and a buddy...but will very likley suffer if you add additional additional crew and gear.

G

[fly4navy]

Best thing to do (obviously) is take it for a test ride with your max anticipated load.

Good luck

[bitsamonkey]

I think any Seacraft fan owes it to themselves to experience the performance of this hull with a very light outboard. Light, I can cruise mine at 28 mph and top out at 38 mph. More of a load and I cruise 25-26. It's an 18 and no top. That OMC 90 is even lighter than my outboard, but probably slightly down on power and won't spin to 6300 rpm. Unless you have some very long runs in sheltered water I would take a chance on that power.

[Bushwacker]

When folks start asking about how a SeaCraft will perform with a relatively small lightweight outboard, they need to recognize that back in the early-mid 60’s when Carl Moesly designed the 21 and 19/20' boats and came up with the unique Variable Deadrise Hull (VDH), THAT’S ALL THAT WAS AVAILABLE! They were DESIGNED for small lightweight motors! The biggest outboards available back then were the I-6 Merc and the V-4 OMC, both of which weighed less than 300 lbs and put out no more than about 100-120 HP! The most exceptional result of the design was that not only did it ride as well or better in rough seas than other more extreme deep-V’s with higher deadrise, it also could plane at much lower speeds with heavier loads than competitive designs with the same power! The average boater that’s not familiar with this history probably has no idea how efficient the SeaCraft hull is compared to most of the competition! And it's unfortunate how many folks ruin this characteristic, screwing up the boat's CG by installing such big motors that are MUCH heavier that what they were originally designed for!

You can learn a lot more about how efficient the SeaCraft VDH is if you read “The Amazing Mr. Moesly” article by Steve D. Antonio in “Professional BoatBuilder” magazine (you can find it in the Literature section on CSC or on Carla’s website @ http://www.moeslyseacraft.com/upload...oeslyp1-16.jpg.) About halfway through the article, there’s a great story about a competition conducted in the early 60’s on Biscayne Bay between the Moesly 21 and a couple of other boats with successful racing histories (I’m guessing maybe Bertram and Magnum or Formula) by a “secretive government agency”. The government had specified the use of a particular V-8 I/O power plant, and required that they be able to carry 9 people and several hundred pounds of sandbags to simulate a certain amount of gear and cruise at a certain speed. The Moesly 21 met all performance requirements but neither of the other boats could even get on plane with the required load! The story relates how Moesly offered to “help” his competition by taking one passenger and several sandbags off of each of the other boats, but they still couldn’t get on plane! He then took the government agents and the extra passengers for a ride around the bay on his now “overloaded” 21, showing that he had no problems getting on plane or holding a good cruise speed with the extra load! Needless to say, he won the contract on the spot for a significant number of 21’ and later 27’ boats that were supposedly used for “covert activities” roughly around the time period of the Bay of Pigs incident! A friend of mine that owned a Moesly 21 and whose dad originally owned my Seafari, told me that he once saw one of those government 21’s at Brown & Hauptner Marine where I bought my boat, with a bunch of steel reinforcement up under the front deck. Turns out it was a mount for a .50 cal machine gun!

Some later SeaCraft brochures claimed that the VDH design, with the same weight and horsepower, was about 10% faster than comparable deep-V’s of the day. I suspect this claim is based partially on the above story, along with the results of much testing that Moesly did at Lake X in preparation for the many races he entered. I’ve noticed one subtle detail in the 19 & 20’ hulls, that may also be present in the 21, 25 Seafari, and 27’ hulls, that might explain this exceptional performance . . . if you sight back aft along the chine towards the transom, you’ll notice that the last 10' of the outer panel angles down, to create a slight wedge shape. This would act like a trim tab to provide extra lift to help get on plane at low speed, but the outer panel is almost completely out of the water at speeds over about 40 mph, so this feature would cause no additional drag or have any impact on top speed! This is but one example of the many subtle but brilliant ideas that went into Moesly’s designs! Denny

[Bushwacker]

Originally Posted by bluefishing

I am looking at a 20' seacraft center console that is powered with a 1980's evinrude 90hp. Can this motor plane this boat?. . .

Thanks

Sometime in the 1980's, all OB manufacturers changed the HP rating system from the power head to the prop. There can easily be losses of 10% or so in the water pump and gearbox, so IF that "90" is prop HP and motor has good compression, it's quite a bit stronger than the "85 HP" motors that were originally installed on new boats back in the 60's and 70's!

I'd have no concern with that rig, PLUS it will ride better and plane at lower speed than a similar boat with a modern 500 lb 4 stroke because it's CG/balance is much better!

[bluefishing]

Bushwacker,

wow, thanks for the history, I never knew any of that. The prop horsepower vs. powerhead horsepower is illuminating and re assuring. When I check out the boat hopefully if everything else checks out, I will buy it!!!

thanks again