Proper HP for a Boston Whaler

[Sailuke]

Hello. so me and a friend are planning on installing a diesel inboard engine on a 16 foot boston whaler. I'm wondering what horse power would be appropriate for this configuration. Also if there are any good sites you know where I can pick a repairable diesel (Yanmar or Universal Preferred) for a decent price.

[GILow]

Well, I can tell you from personal experience, we had one of these in our 16 footer, about 5 HP, and it was not enough when things got nasty. :^)

http://www.oldengine.org/members/kmo.../Blaxland3.JPG

[PortClydeMe]

Originally Posted by Sailuke

Hello. so me and a friend are planning on installing a diesel inboard engine on a 16 foot boston whaler. I'm wondering what horse power would be appropriate for this configuration. Also if there are any good sites you know where I can pick a repairable diesel (Yanmar or Universal Preferred) for a decent price.

An "inboard" on a 16-foot Boston Whaler? What? Which model?

In Port Clyde, Maine, we owned a '69 16-foot "Eastport" model, and a 55hp Johnson OB was just fine. That boat also had a 5.5hp Johnson OB as a back-up engine. We would take many trips far offshore, Monhegan Island, Vinalhaven, etc.

[Sailuke]

No model. Our project is costom installing a reliable diesel into a 16 footer. We would like for it to get up to at least 10 knots maybe 15. I saw a youtube video of a man with an Atomic 4 30hp in a 14 footer and it only went around 8 knots. would we need bigger than 30 hp if it were a diesel?

[CSY Man]

Originally Posted by Sailuke

No model. Our project is costom installing a reliable diesel into a 16 footer. We would like for it to get up to at least 10 knots maybe 15. I saw a youtube video of a man with an Atomic 4 30hp in a 14 footer and it only went around 8 knots. would we need bigger than 30 hp if it were a diesel?

Guessing 10 HP with a special prop with very high pitch.
The question remains: Why?

[PortClydeMe]

Originally Posted by Sailuke

No model. Our project is costom installing a reliable diesel into a 16 footer. We would like for it to get up to at least 10 knots maybe 15. I saw a youtube video of a man with an Atomic 4 30hp in a 14 footer and it only went around 8 knots. would we need bigger than 30 hp if it were a diesel?

No model? Your title states "Boston Whaler", so I presumed an old Eastport. or something similar. AFAIK, all Whalers are designed for OB engines. So the question remains. What? An inboard diesel? Is this a science project? Do you want the boat to plane?

Grab a 50-70hp outboard and be done with it. Whalers are great boats, as is.
Did Maine legalize pot? I haven't been there in a long time.

[ranger58sb]

Originally Posted by Sailuke

Hello. so me and a friend are planning on installing a diesel inboard engine on a 16 foot boston whaler. I'm wondering what horse power would be appropriate for this configuration.

Recently built small boats in the US usually have a tag on the transom that gives minimum, maximum, and sometimes recommended horsepower AND ENGINE WEIGHT.


This would be the same tag that states total number of pax allowed, and total load weight allowed.

Even if yours doesn't have that tag, one may have been on there at one time. If so, a call to Boston Whaler could get you the basic info.

-Chris

[denverd0n]

Originally Posted by ranger42c

...a call to Boston Whaler could get you the basic info.

The basic specifications for the boat, yeah, probably. I suspect, however, that if Boston Whaler knew what the OP wants to do, they would want to have nothing to do with it. They would probably say that the boat was designed to be used with an outboard, and their only comment concerning converting to a diesel inboard would be "not recommended."

(At least, if I was their corporate attorney, that is certainly the advice that I would give them!)

[Mango51]

Take in consideration outboard Hp is rated at prop. While inboards are rated crankshaft.

[Cheechako]

Originally Posted by Sailuke

No model. Our project is costom installing a reliable diesel into a 16 footer. We would like for it to get up to at least 10 knots maybe 15. I saw a youtube video of a man with an Atomic 4 30hp in a 14 footer and it only went around 8 knots. would we need bigger than 30 hp if it were a diesel?

If you don't want to plane then 10HP is enough for sure. Getting up on plane takes a lot of HP. You may find that at 10 knots you are not up and the bow is high. Those are heavy little boats. IF you are doing it I would go with the outboard HP people use to plane them. 50?
If you can find an owner maybe ask what speed the boat comes up on plane at. That might help you figure it out.

[Suijin]

This strikes me as an unlikely and problematic pairing. The Whaler hull is pretty efficient at planing and is a bit of a dog as a displacement hull, plowing a lot of water. If you want it to plane, you're going to be looking at +30hp and the weight is going to kill you. If you don't want it to plane, then why not find a better candidate hull?

Is this one of those "to see what happens" projects, or is the hull sitting available in someone's yard? Is it for a specific purpose? A diesel that is viable is going to cost you more than an old Whaler hull with an outboard that you can fix up.

[PortClydeMe]

Originally Posted by Cheechako

If you don't want to plane then 10HP is enough for sure. Getting up on plane takes a lot of HP. You may find that at 10 knots you are not up and the bow is high. Those are heavy little boats. IF you are doing it I would go with the outboard HP people use to plane them. 50?
If you can find an owner maybe ask what speed the boat comes up on plane at. That might help you figure it out.

A 50hp OB will work. We used a 55hp Johnson, and with 3 in the boat and pulling an adult skier it planed just fine. 60+hp, even better. And, ours was an old Eastport model. Mahogany console & seats, two full tanks .... heavy.

Here's a '70 Eastport with a 70hp Johnson for visual reference.

[ranger58sb]

Originally Posted by denverd0n

The basic specifications for the boat, yeah, probably. I suspect, however, that if Boston Whaler knew what the OP wants to do, they would want to have nothing to do with it.

No reason for OP to become positively loquacious about his intentions.

Basic question gets basic info. Whatever he does from there isn't BW's concern. Which is also their defense, should that eventually be necessary.

-Chris

[PortClydeMe]

Originally Posted by ranger42c

No reason for OP to become positively loquacious about his intentions.

Basic question gets basic info. Whatever he does from there isn't BW's concern. Which is also their defense, should that eventually be necessary.

-Chris

That's a good one. Now chuckling.

[Chuck Hawley]

I'll take a crack at this. Note that I have suspended disbelief as to whether this is a good idea, or possible, or safe.

If you agree that powerboats generally have three modes of operation: displacement, semi-displacement, and planing, you would need three different levels of horsepower to achieve each mode.

For displacement mode, probably any inboard that's on the market could drive this hull to hull speed (say 5 knots). I'd guess that a Yanmar 1GM10 would be grand, or even an old one-cylinder gas engine. So, figure 5-10HP, based more on what's available than what's ideal.

For semi-displacement mode, I'd guess that you'd need from 10-20HP. Semi-displacement mode is generally inefficient, and the pitch angle of the hull is probably uncomfortable, you'd generate a big wake, but it could be done. I'd guess you could achieve 8-9 knots or so.

To plane this boat, I'd guess that you'd need 40HP, and I am not entirely sure that would work. You'll have a shaft angle that is not as efficient as an outboard, quite a bit of weight too far forward, etc. But if you could source a 40HP inboard, it might allow you to plane around 22 knots. Boats of this size generally have a no-man's-land between semi-displacement and planing. You simply can't keep them on a "slow plane" for very long before the fall off the plane and start to mush with their bows in the air.

Presuming you are dedicated to this project, and money's no object, I would find a two-cylinder 2GM20 Yanmar. I think you may have to use a transom-hung rudder (from Buck Algonquin?), since I think the engine well is in the way of installing an inboard rudder shaft, but that depends on the model. Your speed will be around 7 knots (guess) and it might be a fun little "tug" to putz around with. The smaller Whalers have low freeboard, so you might find yourself bailing a lot. Install a large bilge pump aft.

Good luck.

Chuck