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Classic 13-footer Engine Trim
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ContinuousWave Whaler Moderated Discussion Areas
ContinuousWave: Whaler Performance
Classic 13-footer Engine Trim
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| Author | Topic: Classic 13-footer Engine Trim |
| Russ 13 |
posted 03-15-2011 03:34 PM ET (US)  
I realize the [classic Boston Whaler 13-foot hull] has a hooked bottom. The boat seems to require a small amount of negative trim to avoid porpoising at planing speeds. The engine is presently mounted in the third hole set up, and the battery [and] fuel [tank] are moved forward. The [anti-ventilation plate on the outboard engine] while running is under water a few inches. If I run the engine higher (top hole set) on the transom will this make the need for negative (tucked in) trim more pronounced? |
| Clark Roberts |
posted 03-20-2011 05:27 AM ET (US)
Negative trim is normal when engine is mounted low. If you raise engine so that the anti-cavitation plate is about an inch above keel and install a "Doel-Fin" then you should be able to trim engine out. This will result in less draft, more speed (due to less wetted bottom) and most likely better handling. Clark |
| Russ 13 |
posted 03-20-2011 07:47 AM ET (US)
The engine was set in the next to highest mounting hole set. The engine has a set of wedges between it and the hull, to reduce the transom angle, but they add a small setback to the engine. I moved it to the top hole set. Will see if this helps today. Thanks for the advice. |
| jimh |
posted 03-20-2011 09:03 AM ET (US)
The general reference for engine mounting height is in units of "holes" which are 3/4-inch increments. The reference for engine position is in terms of how many units of "holes" the engine mounting height has been raised from the lowest possible position. Please use this terminology and reference for position so that we can more easily understand where you have mounted the engine. |
| jimh |
posted 03-20-2011 12:57 PM ET (US)
Also, to be more clear, we measure the engine mounting position by counting up in units of holes from the lowest position, not by counting down from the highest. The number of holes or positions for engine mounting varies among different engines and brands, and it is impossible to deduce the mounting height if one counts down from the highest position unless one already knows how many positions are available in a particular engine. Thus it is much more easily understood if one describes the engine mounting position in terms of units of "holes" or 3/4-inch increments from the lowest position. |
| Russ 13 |
posted 03-20-2011 11:13 PM ET (US)
Ok, here goes the Hole update. I have a 2002 Yamaha 50 Hp. 2 stroke on my 13'. I know it's a little big in HP, but was the best used engine available at the time. It has four top mounting holes & the bottom mount is a slot. Original set up was the third hole, for the top mount. Changed to the fourth hole, highest setting, and ran boat today. *What a difference 3/4 of an inch made! Much better bow lift with trim, and less negitive trim needed, when on a plane. Prop still has good grip, with no blow-out problems. Porpoising was also reduced. The cavitation plate now is roughly 3/4 of an inch above the boats bottom at the stern. Measured with a four foot level, held parallel to the boats bottom. Again Thank you for the above advice, should have tried this when I first mounted the engine. |
| jimh |
posted 03-20-2011 11:16 PM ET (US)
Russ- You still don't have the mounting height description correct. Just tell us how many units of 3/4-inch or "holes" you have raised the engine from the lowest mounting position. |
| jimh |
posted 03-20-2011 11:20 PM ET (US)
Also, it is best to describe the position of the anti-ventilation (A-V) plate with reference to the water flowing past the engine while running, as you did in your first post. Typically the anti-ventilation plate will be very near to the surface of the water when the boat is on plane and the engine has been trimmed properly. There is a nice collection of photographs that show the relationship between the anti-ventilation plate and the water flowing past the engine in another discussion; see: A-V Plate Pictures |
| Russ 13 |
posted 03-20-2011 11:34 PM ET (US)
ok, The engine is now 3 holes up from the lowest mounting position. Or as high as it will go, with out redrilling the transom. The cavatation plate when trimmed properly is now at the water's surface, when running on a plane. When measured on the trailer, and trimmed parallel to the boats bottom. The cavatation plate is 3/4 of an inch higher than the bottom of the boat at the stern. This change made the boat run MUCH better. |
| jimh |
posted 03-21-2011 07:05 AM ET (US)
Russ-It sounds like you have really dialed-in the engine mounting height on your boat. |
| Russ 13 |
posted 03-21-2011 05:41 PM ET (US)
Thanks Jim. Yes I was supprised how much difference one hole setting made. I guess that is due to the unique bottom design of the 13', and the fact that it is such a small boat. * The A-V or cavitation plate height in relation to the boats bottom, makes a huge difference in how the boat rides, & trims out. |
| Binkster |
posted 03-21-2011 08:30 PM ET (US)
the story goes that the hooked bottom was the idea of Ray Hunt in an attempt to tame the wild ride of the original prototype, and the boat was put into production, without further testing. Back in the day the outboard was just clamped down on the transom, no thoughts of height adjustments. But then 29mph was pretty fast with a `58 35hp Evinrude. |
| dg22 |
posted 03-22-2011 08:06 AM ET (US)
Russ 13, thanks for posting your results on this. I think I'll raise my motor by 3/4 inch. Right now the cavitation plate is approximately level with the bottom of my 13 footer. I had been thinking about doing this but did not think it would make that much of a difference. Glad to hear that it reduced the porpoising. |
| Russ 13 |
posted 03-22-2011 11:07 PM ET (US)
Yes I think you should try it. The changes that worked: Moving the battery under the console, moving the fuel tank forward under the seat. And raising the engine mounting height. The shift of weight forward helped with both static & running trim, plus it created more walkaround space. Now the boat runs good with out porpoising:) |
| Tom W Clark |
posted 03-25-2011 10:51 AM ET (US)
It is hard, in this day an age, to get folks to understand how far recreational boating has come in the last fifty years. The "hook" on the 13 footer's hull had nothing to do with controlling squirrelly behavior. When the 13 foot Whaler was introduced, a 40 horsepower outboard motor was HUGE. It was assumed the 13 footer would be commonly powered by smaller motors for some customers so the hook was molded into hull to promote the ability to plane very easily with as little as 10 HP. A "hook" was very common on all sorts of powerboats back then for exactly this reason. Today, we have outboards of any size you want and you would be hard pressed to find one without power trim. This opens up the possibility of the 13 foot Whaler performing well beyond anything imagined by Dick Fisher in the 1950s. Propeller design has also advanced a great deal in the last fifty years. There is no way an old fashioned propeller from 50 years ago would tolerate the higher motor mounting heights of today's best propellers. Russ -- I'm glad you have raised your motor. It is amazing how much a change as simple as moving the motor up a hole or two can make, isn't it? This simple adjustment, in combination with a well-fit propeller, can offer radical performance improvements for many classic Whalers and is too often under-appreciated. |
| Tohsgib |
posted 03-25-2011 01:27 PM ET (US)
I always said(due to my experiences) that a 13' classic would be hard pressed to hit 40 much less the 45-50mph we uncommonly hear here. I will say that with my heavy as hell 40hp Suzuki all the way up with a 17" Rapure polished SS prop cut down in cup to about a 15.5" equiv. or so she hits 5800 trimmed up with a rooster taim and bimini up doing 37.6. I think with top down I might get close to 40. Before I had prop cut I did about the same as with this 40 and my 40 1994 Evinrude with the same exact prop which was a tad over 37, no bimini, etc. Do I think 40 is possible in a 13'...now I do if set up correctly but even with a 90 I doubt it would hit 50. She can only handle so much and 40 is about it in my opinion. Somebody prove me wrong with a GPS and a video...no hearsay. |
| contender |
posted 03-25-2011 01:40 PM ET (US)
The 13 whaler hull is just not designed to go that fast period. Maybe if you put like a 90 hp on the transom you could obtain it... |
| Binkster |
posted 03-25-2011 07:07 PM ET (US)
"The "hook" on the 13 footer's hull had nothing to do with controlling squirrelly behavior." Well, if do do some research on this site, I believe you will find an article by jimh about the history of the 13 footer where where the hook story is stated. It sounds reasonable and I know of no other planing boats in any time frame that were intentionally designed with a hooked bottom. Builders took great pains to make the aft planing area flat. Most original owners of the first 13 footers powered them with 98lbs OMC big twins 35hp in 1958, I assumed the first prototype was built in `56 or `57 when 30hp was the big deal. Actually the hook would only help a low powered 13 footer if it was powered by a tiller motor and the driver was the only passenger.
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| pcrussell50 |
posted 03-25-2011 08:41 PM ET (US)
Binks! My 1959 "big twin", 35hp Super Seahorse was about 135lbs, IIRC. I think the operators manual said as much. Not sure where you got something under a hundred for the same power just a year or two older? -Peter |
| Russ 13 |
posted 03-26-2011 09:33 PM ET (US)
Going back to the speed idea. Personally 40 mph in a 13' Whaler is WAY fast for that hull. If you removed the hook, then it would get up & go. But the 15' or 17' slightly over powered, is a less squirly platform, to feed the need for speed. Even though I have 50HP on my 13', I usually run around 20 to 30 mph, in that little boat thats enough. And yes the "tuning" with correct engine height & a good stainless prop, makes it run very well. Plus a days running only burns 8 gallons of fuel:) |
| Tohsgib |
posted 03-27-2011 09:25 AM ET (US)
Get a 4 stroke...mine will go all day on 3-4gals. |
| pcrussell50 |
posted 03-27-2011 03:13 PM ET (US)
For going fast, I have boats that are _designed_ to go fast. I don't consider my 1985 Sport 13 to be one of them. For my uses, I -like- the hook. With a light Yamaha 2-stroke 40hp, I can get pretty near as fast as this hull is good for. And since I don't have power trim, I can still run the engine trimmed out for speed via the tilt pin, and with the hook, just a quick goose of the throttle, and shes already up and planing. Works real well. And the motor's so light, its really easy to pull it up by hand, and change the tilt pin. -Peter |
| Prelude |
posted 03-27-2011 05:39 PM ET (US)
Interesting discussion Russ. My 1993 40hp Merc is mounted one hole up from the lowest position on my 1991 13' SS. This put the cav plate in the same, 3/4" above hull bottom, position as yours. I do have 16 gal fuel and battery in the stern. Would have liked to move the fuel forward but the SS storage doesn't allow an under seat tank. |
| Russ 13 |
posted 03-27-2011 08:34 PM ET (US)
I know it is a little on the "out-their" side..... But I had a custom aluminum 12 Gallon fueltank made to fit the area under the seat I have installed. Prior to that I had a 6 gallon tank that almost left me out of fuel a few times. The $200.00 spent was well worth the added capacity & the space gained in the stern. I can now walk 360 degrees around the boat, without stepping on or around the gas tank & battery. And it heped to move some weight forward. |
| Tom W Clark |
posted 03-28-2011 11:10 AM ET (US)
Jim's excellent article on the history of the 13 foot hull is right here: http://continuouswave.com/whaler/reference/13/originalHullDesign.html There is no mention of the hook at all. |
| Binkster |
posted 03-30-2011 10:20 PM ET (US)
Tom, lets not get nick picky, I probably read it in an article on Ray Hunt, or maybe jims interpretation of the article is skewed. His bow on picture of an ORIGINAL 13 footer shows a smirked(later model) hull. What I read is when they changed the shape of the stern keel section they added a hook. You can have the last word though... |
| Binkster |
posted 03-30-2011 10:43 PM ET (US)
Here is an article about the design of the 13 footer written by someone other than jim. I don`t think the hooked stern was designed be accident. It wasn`t there on the original Hickman Sea Sled or the later sea sled design by Ray Hunt. [Fisher had sailboats in mind, but his friend Ray Hunt suggested that there was a larger market for a small outboard boat. Furthermore, Hunt was intrigued with the old Hickman Sea Sled, a design that had a catamaran-type hull. The Sea Sled was a novel idea when it appeared in the 1920s , but never proved to be a commercial success. Fisher soon found out one reason why. After building a version of the Sea Sled developed by Hunt, Fisher discovered that the engine ran unevenly. Too much air was scooped under the center of the hull, causing cavitation problems. He refined the design, finally arriving at one with a pointed keel equal in depth to the side runners. Fisher also devised a unique molding process to build the boat, and by 1956, he had a prototype of the 13 foot Boston Whaler.] |
| Tohsgib |
posted 03-31-2011 09:15 AM ET (US)
What Fisher and Hunt did to the sled was make it a Tri-hull to stop the engine from cavitating. I do not see where that mentions a hook or anything resembling a hook. |
| BQUICK |
posted 03-31-2011 10:34 AM ET (US)
One thing I can say if that my 1971 Sourpuss w/50 Merc(smirked hull) requires alot more trim to get it to run over 40 mph than my 1968 hull. The 71 would literally start to dig the bow in and start to try to plow over 40 until I put power trim on it. Have to run at extreme trim angle to keep the bow up. So, I suspect the later hulls either have more hook than the early non-smirked hulls. (and yes, you can get these things beyond 45 mph (I run 46-49 mph with power trim being the key), don't believe me, fine. I have been running this boat for 40 years, man I feel old all of a sudden!) |
| Binkster |
posted 03-31-2011 11:31 AM ET (US)
What boat designer or builder would openly state that they has to incorporate a hooked bottom to make the boat user friendly. I guess it just appeared one day. I can`t think of another PLANING boat purposely built that way. |
| Tom W Clark |
posted 03-31-2011 12:12 PM ET (US)
Rich -- If you are going to quote somebody, at least have the decency to give the attribution. The article you are using was written by Peter Bohr for the January 1987 Issue of Sea Magazine. Here is an online reproduction of it: http://www.seamagazine.com/boattests/DM_article.asp?id=375 Apart from a few factual errors, it is a good article for anybody interested in the history of Boston Whalers. As Nick correctly points out, the article includes no discussion of the 13 footer's hook. The modification from the Hickman Sea Sled idea to the Boston Whaler hull form was the addition of the third sponson, making the catamaran-style Sea Sled into the familiar cathedral tri-hull Whaler. As I have already said, adding a little hook to a hull was a common trick long ago. My brother-in-law has a MacKenzie Bass Boat that he rebuilt. That hull was built with a hook in the bottom to help it plane easily. When this boat was repowered, a new, much more powerful diesel engine was installed. The boat cannot make good use of the extra power because it will tend to plow if it is pushed faster that it was originally designed to go. This is because of the hook designed into the hull. When I was young, we had a neighbor who had an old 16 foot fiberglass runabout. It was overpowered a Johnson 75 "Stinger" on it that should have made it quite fast because the old hull design was rather flat bottomed. But because of the hook that was designed into the hull, there was an effective a hull speed that could not be exceeded. Applying more throttle just caused the boat to plow more. I used to have an old book that belonged to my grandfather. It was hard-bound and titled (I think) "The Boat Book" and was published in the 1930s. There was chapter in it describing how to make your outboard powered boat faster by building a downward inclined wedge onto the stern of the hull's bottom. Essentially this was a "hook" or permanent trim tab that would help get a boat that could only semi-plan up onto a full plane and greatly increase its speed. I wish I could find that old book. It was a fascinating look back through time at very early recreational boating. Things have changed a lot since then. |
| Binkster |
posted 03-31-2011 03:42 PM ET (US)
Tom, Apparently you found a couple of dogs that needed a hook to get up on plane. Your grandfathers old book would be interesting to read. A semi displacement hull might be able to semi plane with a wedge built into it, as a displacement hull will squat with too much power, and the wedge might lift the stern somewhat. but like you said things have changed. The similar 16` hull as far as I know doesn't have a hooked bottom. When I restored my 13 footer, I contemplated griding the hook off, but is starts a bit forward of the stern, and I figured I would have to grind into the foam and reshape everthing, and the hook was there for a purpose anyway. Might ruin the boat. |
| Tom W Clark |
posted 04-01-2011 10:12 AM ET (US)
Yeah, the classic 13 foot Boston Whaler and the classic MacKenzie Cuttyhunk Bass Boat, a couple of real dogs! The reason the hook is not mentioned in any of the articles cited above is that the hook is unremarkable. It was commonly used fifty years ago. |
| Tom W Clark |
posted 04-01-2011 10:22 AM ET (US)
In the back of the April issue of Yachting Magazine, editor-at-large Jay Coyle writes a highly amusing piece about modern tenders and water toys on yachts and the absurdity of some of them. At the end of his column he writes:
quote: |
| Binkster |
posted 04-09-2011 10:18 PM ET (US)
Tom, you must have been a lawyer in a past life, by the way you can misconstrue comments. I asked you if you knew of any other boats purposely built with a wedge or hooked bottom, I never implied the 13 foot Whaler was a dog and your other comment ; "The reason the hook is not mentioned in any of the articles cited above is that the hook is unremarkable. It was commonly used fifty years ago." is totally not true. I was around boats when they were commonly built from wood (plywood or planked) and yards and owners were very careful how they were stored as wooden boats can develop a hook very easy when stored wrong, and then it was a one way trip to the burn pile. |
| Tohsgib |
posted 04-10-2011 01:17 PM ET (US)
Binks...you got balls telling people that THEY misconstrue comments. My 1994 Hydra-Sports 20' CC had 2 hooks on each corner chine in the stern about 6" long. The only reason I know is that I had to use wedges when I blocked it up for the winter. My 24 Baja had the same thing but not as deep so we were able to grind them off and gel it to look new which helped the performance. Baja used them because not everyone optioned for the trim tabs which I had. My Hydra had them due to porpoising problems but I still needed to use a doel-fin because I never got around to buying tabs which the boat greatly needs. My 13 I do not think has hooks, I will look. |
| Binkster |
posted 04-10-2011 02:26 PM ET (US)
Nick, I don`t agree with you, I`m not trying to misconstrue anything. I think you are confusing wedges built into the bottom at the chines with a true hook which is in the keel area at the stern. The reason for the wedges at the chine in the stern is to keep the bow down on turns and to stop porpoising in turns. They only are used on performance or race boats. The 18 foot Cobia Bass boat I restored had wedges on the bottom of both chines and a padded bottom, however my Class F Racing runabout only has a wedge on the port side chine becuase the boat was designed to turn left only. I know they work becuase the boat is a bear to turn right as speed, with almost uncontrollable porpoising and chine bounce, (chine walk). Below is an article written by a race boat builder who is trying to make his boats turn better. http://www.dillon-racing.com/mini-vee/plans/mini-vee-page-05A.htm Run a straight edge on the bottom next to the keel, and see if there is a depression in the bottom forward of the keel. I know your boat is a later model, but my daughter`s `76 13 footer is sitting on a trailer in my back yard. I will run out and check her boat. |
| Tom W Clark |
posted 04-10-2011 05:12 PM ET (US)
*sigh* I agree that the hook in the 13 foot Whaler is there for a reason. As I have already pointed out, it helps the boat plane with less horsepower. It has nothing to do with taming porpoising. I never said "most small boats were designed this way back in the day." Please do not put words in my mouth. I said a hook in the hull was common and unremarkable. It was not a rare or revolutionary idea. |
| Binkster |
posted 04-10-2011 10:41 PM ET (US)
Better we just leave this topic alone. we`re just repeating ourselves. Better we all get along. |
| Russ 13 |
posted 04-11-2011 04:25 PM ET (US)
Yes, the bottom is hooked. Like all of us with our Whalers. I would also agree that shifting weight forward, tends to eliminate or reduce porpoising. I have found that V hulls do not seem to be as sensitive to this porpoising, as the smaller classic Whalers. Although my experiance with V hulls, have all been longer than 16'. IF Boston Whaler had used the same hull form on the 13' that they used on the 15', it would have ridden better. Just my seat of the pants engineering:) |
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