The 15-foot and 17-foot hulls both do about 34 MPH with a 50 HP engine. The only reason I can think of for this enigma is that 50 HP is not enough for the 15 to get into its performance band (not enough power to lift hull to point of max performance/minimum hull resistance), and that 50 HP is enough to reach "hull high" attitude on the 17 due to its broad planing surfaces (compared to the 15's deeper V and minimal flat planing surface.
If you increase power to 70 HP then the 15 will actually fly and climb so high that only a small pad of hull is in the water. The same 70 HP on the 17 will perform brilliantly but not enough power to lift the 17 hull much more than the 50 HP. A 90- or 100 HP engine will lift the 17 but it doesn't like it, and the 17 will start to porpoise up and down or "chine walk" in a way, complaining that "air time" is not its thing.
On the other hand, the 15-foot hull loves "air time" and doesn't tend to porpoise so long as fore/aft weight distribution is favorable. Max performance is, after all, a function of proper engine set-up (height on transom, jack plate, tune, proper trim, etc.), hull condition, weight distribution, optimum prop type and pitch, good fuel, and so on.
By way of comparrison, I have a 15 with a 40 HP four cylinder Merc, raised about 5 inches on a "Bob's" Jack Plate MJ-5, turning a Yamaha 14" cleaver type ss prop that will run with most 15's with 50+ HP. But if I put 3 adults aboard it doesn't perform very well at all! It's a great one or two passenger rig. If I normally carried a heavy load I would need more "power". The intended use will drive the decision on power. The 17 is more forgiving than the 15 when adding weight as it has tremendous load carring capacity, and the 15 is very sensitive to port/starboard trim and added weight.
Clark Roberts; E-Mail: firstname.lastname@example.org
I got my boys a 1990 GLS 15 with a 2007 Honda BF50 last year, and they spent the summer in Marblehead, Massachusetts, blasting around the North Shore. As luck would have it, a friend of theirs has a Montauk 17 with the exact same Honda BF 50 motor—same year as well. Needless to say, it didn't take them too long before they were drag racing each other all around the outer harbor. And the outcome was always the same: the 15-foot Whaler wins going away. While I think the comments by Clark Roberts are striking and in a way controversial, and I am sure it is his sincere belief that they go roughly the same speed, it has been my experience that it is simply not true. And I believe that is based primarily on simple physics. A 17-foot Montauk weighs over 800-lbs, while a 15-footSport weighs 500-lbs and change. Regardless of the hull shape, those 300 pounds against a 50-HP motor will most likely rule the race.
"I grew up on the Severn River, a tributary of the Chesapeake Bay near Annapolis, Maryland When I was about 14, my parents purchased a new 1983 Whaler 15 Sport. It was definitely one of the best investments they made in my (and my sisters') childhood. My two younger sisters and I spent summers in sailing school in Annapolis, a four mile ride down the Severn. The Whaler was our transportation to and from sailing school, friend's houses, and summer jobs in Annapolis. It gave us kids a tremendous sense of independence, not to mention some just plain fun water skiing after school and all summer long. We were taught by my father to be self sufficient, responsible boaters at a very early age, and looking back, I have to admit that his trust was well founded. We valued our independence, and used it responsibly. Even though I haven't lived in Maryland since leaving for college, I still return for at least a week in the summer to visit family and friends. The 15 is still at the dock, now on a lift since it is not used nearly as much as it was in its early days.
"We purchased the Whaler 15 in 1983 with a 70 HP Mercury. The Merc was never set up right, and I can't recall why, but it was in and out of the shop at least six times that first summer, and the dealer finally put a new '84 Merc 70 HP on it under warranty the first winter. The following summer we had better performance with the engine, but still more trouble than you would expect for a brand new motor. The third summer we traded the motor for a 70 HP Yamaha. No problems. That motor is still on the boat today, and still highly reliable.
"The Mercs were always a little faster than the Yamaha. The speedo on the boat (terrible by comparison to todays handheld GPS's) told us we would hit 47 MPH with the Mercs. The Yamaha would hit about 44 when new. My guess is both figures are about 3-5 MPH higher than true speed, but who knows. The difference in pulling power was night and day. While the Merc would pull up a slalom skier, it was definitely maxed out. The Yamaha didn't seem to care what was dragging behind the boat, it just got up and went. In one case, I remember pulling two slalom skiers out of the water, with three people in the boat. Incredible for a 15 foot boat. Over the years, the motor's strength has deteriorated somewhat. We have swapped to a lower pitch prop to maintain its ability to pull a skier--the skiers seem to be getting heavier, too--at the price of top speed. The 14 year old motor will still pull me (175 lbs) out of the water adequately, and top speed is about 36 mph. Not bad for the old girl.
"The boat is used about 10 days a year now, covered and lifted out of the water when not used. My dad is talking about repowering, possibly with a 4-stroke. I can't help thinking that the boat is looking forward to the increased use it will get when my son is old enough to ski, explore, and just mess around on the Severn River. He was just born this summer, so it will be a few years, but the Whaler will be ready!
"I moved to a lake in Maine about 5 years ago, and tried to bring the 15 up with me. My parents would have no part of that plan. Even though it only gets taken out about 10 days a year, they want it as bait to keep the kids (and grandkids now) coming home. So, this summer I finally bought my own Whaler, choosing a '91 17 Outrage which has proven to be great for skiing and messing around on the lake, but rugged enough to take down to the coast for exploring on nice days."
Doug Merrill E-mail: email@example.com
My 1985 Whaler 15-Sport will hit 49 MPH with a 70 HP Johnson turning a 13-1/4" x 19" stainless prop. At this speed absolute glassy water is a must, and chine walking is considerable. My Dad clocked this speed on the speedo reading of my Eagle depth finder. At 35 MPH the depth finder reads consistent with my GPS, so I think this is fairly accurate at higher speeds. Needless to say, taking your eyes off the water in front of you to read a 1/4" display on a handheld GPS is not a good idea running above 40 MPH. The speedo readout on the depth finder is 1/2" lettering, so it's much easier to read.
Mark Wendt; E-Mail: