How to determine the proper size outboard

[trsexton]

How do you determine the proper size outboard. I have a 17 ft BellBoy with a small cuddy cabin. And how big should a kicker be ?

Tom

[Lootas1]

I have a 17 foot Larson with a small cabin and am running a Merc 650. That is about as small as I would want on it. I think something around 10 hp is best if you will be running on saltwater sometimes against a strong current. Maybe 5 hp would do on a lake.

[Marty Loken (Norseboater)]

Outboard for a 17-foot Bell Boy

Tom -

I ran a 50 Honda four-stroke on a 19-foot Sabrecraft Catalina express cruiser--very similar to your Bell Boy--and was satisfied with performance. Got 26 mph on the GPS, running alone without a lot of extra weight in the boat. But a 60 or 75 would have been better in terms of providing some reserve power...so that you can achieve a decent, all-day cruising speed at about three-quarter throttle, saving on fuel and reducing engine noise considerably.

Having said that, I early had a new 115-hp four-stroke on a 17-foot Skagit express, but that was obviously overkill in every respect. The boat handled the power okay, but I had way more power, motor weight and engine retail cost than was needed for the little 17-footer. (My rationale at the time was that I could always use the 115 later on a larger boat, but fate intervened and I ended up selling the 17 with the 115.)

This year I'm working on an 18-foot Bell Boy express that'll be powered--ideally, I think--with a 60-hp Yamaha four-stroke.

As you probably know, the horsepower rating of modern outboards is measured at the prop, whereas with vintage outboards (from the 1950's and 1960's) the power was rated at the flywheel...which means that the new engines put out more thrust per horsepower rating than old motors. A new 50 hp will always push your boat with more power than a vintage 50 hp, generally speaking.

As to kicker motors, what a subject! As Jerry says, you might want a bit of extra oomph if fishing in saltwater currents, etc., but I have a personal dislike for kickers hanging on brackets off the transoms of vintage boats, and prefer to carry a very small and lightweight 2-4 hp kicker inside the boat, under a seat, to be used only as an emergency "get home" motor. So it just depends on your particular need. For a lot of fishing, an electric-start 8-9.9 hp kicker is great, but if it's only for emergency get-home use, you might want to consider something smaller.

- Marty

[Helmar]

There is no such thing as too much power.
NO WAIT, that was To much Fire Power.

My little 16 foot Skimaster will do 25mph sipping fuel with a 55 Bearcat engine.
On my 20 Skagit offshore, I have a 100hp Volvo Penta that pushes her right alone at about 28mph with a 15hp small package kicker.
I had to use it a couple of times and it surprised me how well it pushed that boat into the wind.

[halffast32]

A 17 footer probably needs at least a 5hp and at most a 15. I have a 10hp on my Seafair Sunliner and it will troll down pretty slow, but can still move it fast enough to get back to the dock in a timely manner if required.

[westerner]

I originally mounted a kicker for fishing in the sound and emergency purposes. Use it far more than my main motor. I have a 16' boat with practically the same hull as a same period Bellboy and my 8hp four stroke seems to be just right. With two people and all my gear I get 7-8 mph according to gps and depending on tide direction. I've seen the same motor on a 19' Bayliner Trophy so I guess it all depends on how you're going to use it.

[McSkagit Tim Jones]

My experience with kicker motors is that it takes more power than you might think if you are going to use it as a "get home" motor. If the water gets rough or there is a lot of wind and/or current, your motor will seem anemic. Often because the kicker is mounted so far aft, pitching will result in the propeller leaving the water causing airation (loss of traction). More power and a long shaft is better.

I've also towed in a few boats over the years that ran out of gas trying to get home on the kicker. With a four stroke you can pull fuel from the main fuel tank presuming it's not contaminated or empty.

On the main engine, more power is better. Although heavier and more expensive, the more powerful engine turns slower therefore last longer.

Many years ago a customer had a 25 Bayliner with a 305 Chev/Volvo I/O. He had quite a few problems with that engine due to poor exhaust manifold design. He finally repowered with a 350 Chev V-8. With more torque and bigger prop the engine turned slower (quieter) and used 20% less fuel for the same speed.

McSkagit

[ChuckB]

Tom:
I now own the 19' Sabrecraft Marty referenced. I too have a 50 Honda on it, and even after adding a fair amount of weight, I GPS at 29mph @ 6000rpm.
The same motor on a 16' Glasspar did 34 mph @6k. A 9.5 evinrude kicker motor pushed the glasspar to just planing speed. I had a 75hp 3 cyl 2 cycle on the Gspar as well and turned 42mph but with a considerable sucking sound from the fuel tank going for my wallet. The 75 was nice and fast and LOUD, and thirsty, best was about 4 mpg. the Honda gets about 8 on the Sabrecraft, more than 10 on the 16' Gspar.
Hope all that helps, ChuckB

[trsexton]

Thanks to all for the replies it really helps. Looks like for now I will purchase a kicker and leave the 75 hp Mariner on as long as I can get it to start on a regular basis.

Tom

In the "Safe Powering" section of the USCG Boatbuilder's Handbook there's a specific formula for calculating outboard horsepower capacity. This formula should apply to the hull/motor configuration most of you have.
http://tinyurl.com/9hgvvw
Scroll down to section 183.53 for the outboard formula.

While gov't regulation is never a popular topic, and is often fraught with error, I stongly feel that this and many other USCG saftey regulations are spot on. Besides the obvious safety aspect of getting ob power/weight correct for any given craft, I've found that overpowering some craft with an outboard of excessive weight causes trim and efficiency problems. In the case of the Bartenders we've seen many examples of owners following the "more is better" theory of powering. What follows is an ugly series of ill-conceived modifications which negatively affect the safety and performance of the boat. Sadly enough, many are talked into outboards which are not suitable for the boat by outboard dealers who have no experience with powering easily driven designs from another era.

[BellBoyBob]

I have the 19' Bellboy Express and it came in 1960 with a Merc 800 (80 hp) "dock-wrecker". It then went to a Merc 850 from 1964 and that pushed it at 31 mph. It now has the Merc 1350 (135 hp) from 1970 and I am just under 40 mph with that one turning a 13x15 three-blade prop. It was overpowered because my dad wanted to pull up all three of his sons at the same time on single skis from a deep water start. He did!!! over-powered, of course but it is a 2 cycle and not too tough on gas economy (6 gollons / hr at cruise )
My kicker is the Merc 110 (9.8 hp) from 1962. This pushes the BB at 5 mph in calm water.

[Yardman]

Bob, That is one clean looking BellBoy. Nice job. When you went through the transom to run your transducer wire how did you seal her up? - Ross

I borrowed this from another site ---- http://www.tinboats.net/forum/viewtopic.php?f=4&t=12144


Hopefully this guide will help you calculate the maximum amount of H.P. your boat can be insured for.
- This is to only be used as a guide.
- You can round your final HP number to the closest multiple of 5. (31 HP would round to 30 HP. 33 HP would round to 35 HP)


Step One - Compute your Factor

A. Length of Boat x Transom Width (measure in feet: 14, 15.5,16, etc).



Step Two - Compare your factor to H.P. rating

A. 0-35 = 3 hp
B. 36-39 = 5 hp
C. 40-42 = 7.5 hp
D. 43-45 = 10 hp
E. 46-52 = 15 hp



Step Three - If your factor is over 52 (Choose only A or B)

A. With Remote Steering (steering wheel) and at least 20" transom height

Maximum HP = (Your factor x 2) - 90

Example: 19' 6" long , 7 feet wide = (19.5 x 7 x 2) - 90 = 183 (Round up in multiples of 5. This boat's max is 185 hp).


B. With Tiller Steering (hand or extension) or less than 20" transom height (Choose only 1 or 2)

1. Flat bottom, or hard chined boats (hull has hard angles)

Max HP = (Your factor x 0.5) - 15

2. Soft chine, rounded hulls

Max HP = (Your factor x 0.8) - 25


Conclusion

I hope this has helped you all who are looking for max hp ratings. If your boat is insured, make sure to check with your insurance company for any restrictions.

This guide was found at NewBoatBuilders, which was ultimately used from "Title 33-Code of Federal Regulations-Subpart 183.53".

[Tim McCrain]

Excellent post, thanks for the good info.

:GoodJob:

[Bob Bobbers]

lots of choices

i had a 57 skagit 20' cuddy and hung a 90 hp merc on the back.
RARELY was I able use full power in the salt water. (skagits ride a bit rough)
I am restoring another 20 footer and will step down to the 50 - 60 hp range for this one.
I also ran a 9.8 kicker and was real happy with that.

Remember, these older boats were hull designed for more "cruise" than hauling butt. Most boats of this era came with 18 hp - 25 hp twins from the factory!