1984 SPORT 15 Re-power

[K wester]

Give me advice about choosing an new engine to re-power my 1984 SPORT 15.

BACKSTORY

I just purchased a 1984 SPORT 15.

I [was planning to re-power with a new 90-HP engine mounted on a jack plate, either a Yamaha or a Suzuki].

[A dealer told me] he had re-powered multiple boats like [a SPORT 15 using a Yamaha] 70-HP engine, [not using a] jack plate, and [also installing spring-loaded non-adjustable trim tabs].

[This dealer also noted the 70-HP engine would weigh 80-lbs less than the 90-HP engine and would reduce the weight in the stern.] [The dealer said the reduction of weight on the transom would reduce the tendency for the bow to oscillate up and down when the boat was on plane.]

[Moderator’s note: an extensive re-write of this post was necessary to conform to the use of written English language in the forum. See https://continuouswave.com/forum/viewto ... 844#p21671 for advice.]

[Jefecinco]

I would have doubts about advice from a salesman who recommends an engine which needs trim tabs. A properly powered 15 foot boat should not need trim tabs.

Q1: why do you feel a jack plate is needed?

[jimh]

A SPORT 15 is really only comfortable for two people aboard, particularly when operating at any speed.

For general use a 70-HP engine will provide very good performance, will be less expensive than a 90-HP engine, and will eliminate problem created by excess transom weight as would occur with your scheme to over-power with a 90-HP engine mounted on a jack plate.

[K wester]

I want the SPORT 15 to be able to get onto sand bars or spoil islands in the Clearwater, Florida area.

I tend to over-think and over-build my projects.

I am not really interested in maximum boat speed, but I don't want the boat to be under-powered.

I think the SPORT 15 hull might become a bit unstable at boat speeds above 45-MPH.

[Moderator's note: again, this post has been completely re-written in order to obtain the minimum necessary form of written English used in this forum.}

[jimh]

With the outboard engine tilted up, the draft of a SPORT 15 will be probably less than one foot. Getting ashore on a sand bar will not be a problem. A jack plate, if anything, will increase the draft in the stern and make getting onto a sand bar more difficult.

ADDITIONALLY

The point I am making is for the circumstances as I indicated in the first sentence, viz. WITH THE OUTBOARD ENGINE TILTED UP.

At that pont the jack plate does NOTHING to decrease draft, and does the exact opposite. The added weight INCREASES DRAFT.

[dtmackey]

With the outboard engine tilted up, the draft of a SPORT 15 will probably less than one foot. Getting ashore on a sand bar will not be a problem. A jack plate, if anything, will increase the draft in the stern and make getting onto a sand bar more difficult.

A jackplate will allow the motor to be run in shallower water on plane as the motor can be raised (vertically) almost [three times higher than] the highest mounting when attached directly to the transom.


Fig. 1. A full six-inches or more above the transom.


Fig. 2.


Fig. 3.

Figures 1, 2, and 3 show my 1986 SuperSport 15 with an Atlas Microjacker jack plate. I am very happy with the unit.

D-

[jimh]

If you think you MUST have a jack plate, then the only SENSIBLE choice is get one that can be adjusted electrically and while the boat is in operation. A fixed jack plate might be useful if for some reason you wanted to ALWAYS operate the engine at an engine mounting height greater than four-holes-up, but that is a very unusual and unlikely situation.

But I don’t think anyone really plans to run a SPORT 15 ashore onto a spoil island under power and on plane. I would think that is a rather odd way to beach the boat. A fiberglass boat bottom is not going to appreciate being driven under power onto sand and shells.

[K wester]

The jack plate I would be getting would be one with an electric motor to adjust height.

I don’t know the weights of all the various models and brands of jack plates.

I plan to buy a Yamaha 70-HP engine.

[Kapharms]

I have a 1977 Sport 15 with an aftermarket center console. A SUZUKI 60-HP engine [provides good performance when the boat has a] full load.

The 60-HP engine can accelerate the 1977 SPORT 15 unto hydroplane without any concern. [An unspecified boat speed at] cruise [is] easy [to obtain].

A Yamaha 70-HP engine is ample power and there is no need for a jack plate, as long as you do not intend to pull water skiers or intend to pull a water toy tube.

[K wester]

I have ordered an Atlas atlas jack plate [of unspecified model].

[jimh]

I have ordered an Atlas atlas jack plate [of unspecified model].

Please indicate which model.

[jimh]

Here is another anecdotal performance report:

I owned a 1976 SPORT 15 with a 1976 MERCURY 50-HP four-cylinder 44-cubic-inch two-stroke-power-cycle engine with carburetors, without power-trim, with manual tilt, with the engine mounting height in the the lowest position, with the engine trim-position fixed and not adjustable while underway, with a random three-bladed aluminum propeller that cost $40, and without any trim tabs.

With two adults aboard the boat was able to accelerate onto plane effortlessly, and driving the boat was like driving a sports car.

The fuel economy was so fantastic I never gave a single thought about the cost to run the boat.

With two six gallon fuel tanks we could cruise around all day—well, cruise around until our backs and butts got tired of sitting on the thwart seats with no seat backs, which was a duration of several hours. We loved the boat, and I regret selling it.

The Boston Whaler classic 15-foot hull is a wonderful design and is probably the best 15-foot boat ever made.

I loved the simplicity of the boat. The mechanical cable steering was really completely sufficient. One battery was all that was needed. The boat on its trailer fit in my standard-size 1950’s garage, and I could tow it on the highway with my FORD four-door V8 sedan that was my daily driver.

We never gave a thought to pulling an adult water skier—let alone gave thought to ever towing multiple water skiers simultaneously—in part because all the adults we know have no interest in water skiing, and further I would NOT think of using a SPORT 15 for water skiing because of the hull’s round bottom.

Similarly I never gave a thought to pulling kids around while they were sitting inside or sitting atop or dangerously clinging to weirdly colored and shaped water toys while I annoyed the shoreline property owners by roaring by too close to their docks while pulling screaming ten-year-olds, and mostly because to me it seems such a stupid form of recreation on the water.

ASIDE: if you want to enjoy boating with your kids, teach them how to operate the boat and let them operate the boat under your supervision, and if they show they have learned to operate the boat properly, let them operate the boat by themselves and run the boat while you supervise from shore.

[dtmackey]

I have ordered an Atlas atlas jack plate [of unspecified model].

The Atlas Micro Jacker is the perfect combination and weighs in at 23-lbs. I mounted all the control relays under the engine cowling. The jack plate UP-DOWN control switch is mounted on the Yamaha remote throttle and shift control lever, allowing me to adjust speed, trim, and engine height with my right hand, while keeping my left hand on the wheel.


Fig. 4. The UP and DOWN relays that control the motor for the jack plate are located under the engine cowling


Fig. 5.


Fig. 6. The Yamaha remote throttle and shift control lever modified to include the remote UP and DOWN switches for the jack plate motor.

You will be surprised how much higher you can run the outboard engine [by having an electrically-operated adjustable-height jack plate compared to] having [the outboard engine] bolted directly to the transom. Also, as you raise the engine the steering effort gets lighter, and the steering becomes more responsive. Even at six-inches above the transom, there is no concern with [insufficient volume of] water for engine cooling.

I love the jack plate on my Boston Whaler boat, and I wouldn't have the boat setup any other way. I understand there are people out there that feel it is unnecessary, but I feel [an electrically-operated and adjustable jack plate] improves boat handling and allows for shallow water running which I could not do otherwise.

D-