Small boat w/ big engine

[salmonee]

I just picked up this 78 16' Sailfish with an '04 Yamaha 115 4 stroke outboard. I believe the motor is above the weight limit for that boat but the owner had a steel reinforced plate put in the transom when it was installed. Anyhow, I'm trying to fix the issue with bow rise while getting on plane or just trolling slowly around. Do I go with the hydrafoil or trim tabs? What's the latest news...Will the tabs affect my transducer due to it's location?

Side note: I ordered this easytroll trolling plate which I did not know that I had to drill NEW holes in the cavitation plate to attach to my outboard. Now I'm second guessing whether I want to install it at all. However, the manufacturer do offer this duo doel-fin style/trolling plate as an option. Someone recommend I use bags instead of drilling holes into the cavitation plate. What do you think?

 

[Silvertip]

Re: Small boat w/ big engine

We have several recent discussions regarding insurance on this forum so I need to ask -- is the boat rated for a 115. If so, then that's fine. If not, you are at risk for legal action if you are ever involved in an incident involving property damage and even worse trouble if personal injury is involved. Most trolling plates and fins require drilling of the AV plate.

 

[witenite0560]

Re: Small boat w/ big engine

I have very much the same situation. I bought my boat last summer, a 1968 Crestliner with a 1970 115hp Evinrude. The data plate says the Max HP should be 100hp. I'm in the process of trying to find a motor in the 60hp - 85hp range. I just need something with enough power to get me up on plane to cruise around the lake from place to place for fishing and occasionally pull a tube or something. I have no doubt, after reading about a lot of folks with similar boats who are happy with 50 - 70hp, that my boat is grossly overpowered. Unfortunately, that means I'll never use the top end and am burning far more fuel than I need to. Not to mention potential liability and insurance problems.

 

[erikgreen]

Re: Small boat w/ big engine

It's dangerous too.

Since the boat is rated for a specific HP, it's designed for a certain amount of thrust and a certain engine weight. If the weight is excessive then the boat could be imbalanced, which might just make it handle poorly or it may cause something like a capsize in the wrong conditions.

If the boat is too light for the engine's thrust, it might become very difficult to control at high speed, resulting in "twitchy" control response... again very easy to have an accident.

It's like sports cars... you can stick a v10 supercharged engine in a production sedan, but you'll just get more power, you won't get sports car suspension, sports car brakes, sports car tires, or any of the other design features that let the car use that power safely.

Erik

 

[saumon]

Re: Small boat w/ big engine

Bow rise at under plane speed is absolutely normal and will be more pronounced if the boat is too light for the engine weight/power.

An hydrofoil won't change anything at slower speed. It need some waterflow to work and, if by example you'll previously get on place at 20 mph, maybe you'll now be able to plane at 15 mph. So to speak, the bow rise will last less time.

Best advice i can give is trim it fully in at start-up and gun it then, when on plane, back it off at the sweet spot (you'll eventually find it by ears, something around 3/4 throttle or 4000-4500 rpm) and trim it out until speed stop increasing.