Trolling motor for cabin cruiser

[sutor623]

Re: Trolling motor for cabin cruiser

I was actually impressed at how fast you were going with the 4hp. (3-5 mph?)

Thanks man, Im happy with it. Good math too. I dont know exactly what speed it was going, but it actually went a bit faster when I tilted the motor out of the water. Never GPSed it but Id say around 4mph. I wish I youtubed the vid I had of my 9.9 on the back. That joker planed out my boat!

 

[nphilbro]

Re: Trolling motor for cabin cruiser

I'm in complete agreement with Fireman.

I have a 3000# 19 1/2ft fiberglass with a deep V and run a 15hp longshaft kicker. I was initially looking for a 8hp and the guy I bought it from had both 8 and 15 for sale. The weight of the two was nearly identical so I opted for the 15hp. The 15hp might seem a bit overkill for my boat but it's good to have the extra power when trolling deep in strong Puget Sound tidal currents. I also like the peace of mind it gives me as backup power should the main fail. When dialed in right and fishing lakes at 1 1/2-2mph it will troll forever on very little fuel and still uses less on a 5mph troll in tidal current than the main. Another consideration is the amount of set work involved in changing power powerplants mid-troll due to wind or currents vs. just giving it more throttle.

Something else to consider is the weight of the kicker vs. power output. Since I run Johnson/Evinrude exclusively, 15hp is the top power for the engine form factor and, in my case, moving to a 25hp would mean a lot more added weight since it's essentially adding the weight equivalent of a 50hp.

I've seen many boats similar to the size of yours and 15hp is pretty common. Trolling with downriggers is like dragging an anchor(s) since we use up to 15lb balls out here at times. You could find yourself running a 6hp, maybe even a 10hp well beyond crusing RPMs to get the right trolling speed and the fuel usage would be way more than a larger (15hp) kicker running at optimum RPMs. My kicker also has charging (that I still need to figure out how connect inline without blowing anything on my main) so it adds yet another level of safety and redundancy- including a spare portable tank with regular fuel rotation to the main in case of catastrophic failure at any point in the propulsion/electrical system.

I would, however, recommend one that uses the same fuel as the main, if possible to insure your fuel is fresh due to ethanol.

That's just my 2 cents. Lots of things to consider. Good luck and happy fishing!

 

[ondarvr]

Re: Trolling motor for cabin cruiser

People frequently respond with an answer specific to their own location and type of fish being persued, not with the the answer to the question asked by the OP.

To the OP, we don't know your location or what type of trout you may be after, and there is a huge difference between bodies of water and the specific trout you want to catch.

Will the 6 push your boat, sort of, but you probably wouldn't be satisfied with the results, but since you have it give it a try.

A Yamaha T8 or T9.9 will push it, these have a larger gearcase with a greater reduction and a bigger prop, they are designed to do this exact thing, push large heavy loads. They will even do this much better than most normal motors twice their size. These are the gold standard for trolling motors.

In some places you could troll with one of the mains, and it's done frequently, but depending on the "trout" you are after, and your exact boat, motor, prop, etc it may be far too fast.

 

[UncleWillie]

Re: Trolling motor for cabin cruiser

Power is power!
A 6 hp engine producing 5 hp will move you at the same speed as a 15hp engine producing the same 5 hp.
The 15 hp engine will not be working as hard but it will be using almost the identical amount of fuel to make the 5 hp.

The 15 hp engine has 2.5 time more power available but you will not go 2.5 times faster. (That cube factor again.)
It will take (2^3=)8 times the power (6*8=48hp) to double the 6's speed. (All else being equal, which it isn't.)
The 15 will increase the speed by 36%. (2.5 ^ 0.333 = 1.357)
If the 6 makes 3mph, you could expect no more than 4mph from the 15. (3 * 1.357 = 4.07)

You already have the 6, put it on and run it.
You may be surprised at what the little 6 will do!
If it is just too slow get a 30hp to make it 1.70 times faster.

(Again, All else being equal, which it isn't!)

 

[greenbush future]

Re: Trolling motor for cabin cruiser

How do you plan on steering this new power source? Throttle control too? For me reaching down over the back of the transom to the hand control on the kicker was a real PITA, made my decision really quick and really easy, that kicker didnt work worth a darn on my boat. You cant have a bunch of clutter on the back of your boat using downriggers. One tangle can be very costly.

What about when you fave a fish on, how about when you have a double? I still think I would run the main, much cleaner application.

 

[dingbat]

Re: Trolling motor for cabin cruiser

I was actually impressed at how fast you were going with the 4hp. (3-5 mph?)

Power needed is proportional to the square of the waterline and cube of the speed.
Assuming the 29 has twice the waterline of the 16 and your 6 is 1.5 time the hp of the 4....

(2^.5 / 1.5) ^ 3 = .84

Your 6 should push the 29 footer at ~85% the speed we saw in the video. (2.5-4 mph?)

My physics is old and rusty and someone will correct it, but it does not take much power to move large objects slowly through water.
It DOES take huge power to move even small objects Fast through water. It is that cube factor that kills you.

Those Hugh container ship are some of the most efficient mass movers ever produced.
They can achieve in the neighborhood of 50-100 ton-miles per gallon of fuel.
That is on par with rail transport efficiency.

You calculation accounts for friction caused by the water but not from the wind and waves which would be substantial on the larger boat.

From experience, I need roughly 20-25% more power to troll a #5500 22? boat 2.5-3 kts. on a moderately rough day (10 kts.) than it does on a flat day. Running against a 2 kt tide I can almost double needs.
I run a 15HP troller on a #5500 22? boat. The motor is pretty useless on days when the winds are 10 kts. or better. I can?t imagine trying to use 6 HP on it.

 

[Scott Danforth]

Re: Trolling motor for cabin cruiser

have you thought of troll-n-tabs? I would try to find someone with a 9.9 and try it.

 

[ondarvr]

Re: Trolling motor for cabin cruiser

Its not as simple as a HP=speed formula, the prop and gear reduction differences come into play when pushing a heavy load

 

[laserbrn]

Re: Trolling motor for cabin cruiser

Yeah, none of that really applies on water, but nonetheless the concept is there. Torque is what moves weight, not horsepower and generally the bigger the motor, the more of it you get. I think that a 25 or 30 is probably the minimum to move that big arse boat, but I'm planning a 25hp for my 5500# boat. You may even consider a 50.

 

[Neilmac42]

Re: Trolling motor for cabin cruiser

Thanks everyone your advice has been very helpful. I have decided to use my main motors as they seem to have an ideal idle speed for the lake trout i am going after!!
Cheers